I'm guessing fingerling is reffering to when they are about the size of your finger, that's what I've always thought of it as?
I haven't seen many display tanks with barra in them, only 2 from memory.
I think the main reason being is that they get huge!
Not many people can accomodate a group of large barra...
Personally, I'd rather grow fingerlings into big dispaly fish rather than buying big ones, more fun that way and as Shane said, you can get them pretty cheap when they're small