We have romulan fleet !

Question: the romulan's have a special fleet ?
Answer: the developers, Cryptic, doesn't create a special fleet for romulans

Question: how romulans can join a fleet ?
Answer: When a romulan reached level 10 he must choose sides: Federation or Klingon. 
Based on this choice the romulans can join only a Klingon or Federation fleet, you can join one of our fleets, Klingon or Federation fleets

Question: so, i am a romulan and i choose a side, how can i join a fleet from Deep Space Alliance ?
Answer: you must ask to join a fleet on our shared chat channel: deep space alliance chat. Here is a tutorial, click

The admirals on each fleet can invite you to join

Deep Space Alliance has 5 fleets, so is room for all to join a fleet, we have Klingon fleet and Federation, too.

link here