There is a way of getting more dremora lords. You can dead thrall up to two dremora with 100 conjuration and the top perk. The highest level of dead thrall you can capture is a dremora markynaz mage or warrior. The mages can only be captured during the Black Star Quest and the warriors can be found in a couple of spots but your best bet is at the shrine of Mehrunes Dagon during the pieces of the past quest. Dremora Markynaz will default appear when you are between levels 36 and 46.
Once you have two dremora thralls you can arm each with a copy of the Sanguine Rose. You dupe items by dropping them outside, having a follower pick up the item and then moving inside a building. When you go outside again the item will appear in your follower's inventory and on the ground again. Recover the items and then arm your dremora with a sanguine rose each. You can now effectively have 4 dremora lords on your side. NB although you can only thrall up to dremora markynaz, if you yourself level past 46 then your thralls (who stay as markynaz) will summon creatures based on your level. So at best you can have 2 dremora markynaz and 2 dremora valynaz.
If you want more you can even ritual stone a couple at the atronach forge or arm a follower with a Sanguine Rose as well but then it just gets ridiculous. What can I say, I like my dremora army although they can be a bit OP and they do shout a lot. (XBOX tested)
*For best results arm followers / thralls with different summoning staffs. if they all have the same staff then they will summon creatures a lot less frequently. Thralling NPCs who summon creatures works best - good candidates include the traveller (who summons a gargoyle) and there is a dragon cultist who summons a seeker in Miraak's temple. Necromancers are limited to level 40 daad thralls and note some characters level faster than you do like Ulfric and Vyrthur.