It's all because of their sneaky damn cloaking that they never seem to appear often as doff missions, so many years of battle cloaking has gotten them paranoid to the point of hiding. (sarcasm at no additional charge)
There is a Vendor on New Romulus ... Although she only offers common (white) BoFF's for 204 Dil.
It's a bit hit and miss though, for some reason, and unlike most other BoFF vendors, as far as i'm aware, you can't see what their skills or traits are until you buy them, and they either have "Basic Romulan Operative" or 'Subterfuge" as optional traits.
Good news though, is that they can sell for anywhere from 50K to 100K EC on the Exchange.