You don't need anything else. Generally speaking when there's game content that asserts something about the Elder Scrolls universe and there's no other game content to cast doubt on those assertions it becomes adopted as part of the Elder Scrolls lore. A lot of the lore of the Elder Scrolls universe is single sourced. It would be nice if the developers put multiple sources for every notable aspect of Tamriel but they haven't afforded us that luxury which is why lore resources like the Imperial Library and the Unofficial Elder Scrolls Pages incorporate single sourced information about the Elder Scrolls Universe as long as it is noteworthy, can be conveyed from the perspective of an anonymous citizen of Tamriel, and isn't contradicted by anything else in the game series.
The common understanding is that they're immortal so they don't need to mate. Immortals in general don't appear to mate in the Elder Scrolls universe (Daedra, Aedra etc.). When they do it's in abstract terms that transcend traditional notions of mating such as when Anu and Nir mated and Nir gave birth to Creation.
Why not? He's a god and the notion of a god creating life from nothing other than its power is hardly a novel concept. Akatosh created the dragons in his own image. Does that sound anything like another religious text that you might be familiar with?
How does the absence of evidence to support the notion that Dragon's mate (i.e. eggs) in any way support the notion that they do mate? That's a completely illogical inference to make as the absence of eggs supports the opposite notion. Most people accepted that Dragons of the Elder Scrolls universe don't mate which is why the thread only continued on with posts in jest after the book was mentioned.
There is a series of books found in the game Elder Scrolls II: Daggerfall whose contents are published at the Imperial Library and UESP called King Edward where one of the characters states that, much like elves but even more so, Dragons breed slowly because they are so long lived. However, Marilyn Wasserman, the actual real life author who wrote that book for Daggerfall, has stated that the King Edward series should be regarded as historical novels, not official lore or history. So while the existence of the book itself is lore, the contents of the book have been qualfied by the author as not being lore. In addition we know that the notion that elves breed slower than humans was dispelled in the Pocket Guide to the Empire so it's fair to assume that the fictional author of the book, who was anonymous, was ignorant about a great many things when he or she wrote the novels including the nature of Dragons.
Okay fair enough with the book. However if one were to write an RP or fanfic they could easily get away with putin female dragons in the story. If the player comes across the book, he reads it, it says "So far we have not found any of the dragon eggs YET." Yet is the key word. For all that scholar knows, the dragons could give live birth (highly doubtable though). Or the mother and father destroy the egg shells for some reason after the eggs hatch. Easy explanation for stretching the lore a bit. The only reason I want female dragons is because I based my Dragonborn on being the son of a dragon (don't even ask because seeing as you are a lore whore JK
you would probably laugh). The main reason I'm not a big lore lover, is probably becuse the only ELder Scroll game I have played is Skyrim. :O OMG I know he is a blasphemer! I started playing only because I love dragons and the Argonians were the coolest things ever.
Dragons lives are technically like Orcs, they don't grow old and die. They have to be bested by another dragon. However it seems their power does wane after a while i.e. Paarthurnax was probably stronger back in his glory days under Alduin's command. So when a dragon reaches a certain age, he probably would be more suseptable to another male taking his land (or having one of his sons killing him so they could inherit the territory from their father).
Now like I said, the dragon population would be down if they could not reproduce. You claim they immortal. Wrong, they are partially immortal. They can still die, and their sould gets absorbed by the dragon who killed him. Also they could be slain by mortals (probably not as reassuring as a dragon absorbing the other one's soul, but he is still dead). So if one dies that is one less from the already pretty low population of dragons. How would he come back to life? Other than Alduin (who the dragonborn kills more or less) raising them up. So the dragons would need some way of keeping the population up. I said earlier in one of my posts that it is possible that the females could have low fertility rate and could give birth to only so many dragons in a life time.
Yes, I am familiar with the saying, "Made in His image", but God does not throw humans out of nowhere on the planet. We reproduce. The reason I say Akatosh wouldn't do that is because for starters what would be the point in that? If he made females he wouldn't have to worry about spawning a new dragon every time one dies! So if there are no females, either Akatosh was retarded, or he had nothing better to do. You know he is just the chief deity of the nine divines, he must not have much going on.
Now I get that lore is a major part of writing fanfics (and such) but this is something that all depends upon the writer. Until Bethesda gives us SOLID evidence (other than some ruminescence of some scholar who made assumptions in one book) that there aren't any female dragons, then I refuse to belive they don't mate. However, even if they did say there weren't any females...I would and will still add them in my fanfic.