If I remember correctly (which isn't always a given!) NERD was starting a gerbil-feeder breeding project. They may have some for sale. I think I remember Kara mentioning that.
There's a petstore in Annandale that sells tons of feeders. I don't know if they intentionally breed gerbil feeders, but I know they have a lot of gerbils and they don't hesitate to sell animals for feeding purposes, so you might be able to get some baby gerbils from them in a pinch. Super Petz in Annandale on John Marr Dr.
Gerbils aren't hard to keep at all, though. If I had a picky eater, I would just breed my own.
EDIT: I don't know how close you are to NERD though... I can't locate a place that ships frozen gerbs but I'll keep looking and hopefully I can dig one up.