I'm surprised a Petco had them!!
I was too when I first saw them.
A couple months back, I took a Saturday and visited a few fish stores.
I went to Fishy Business, Petland (on semoran near the airport), Pet Bazaar and Petco in Altamonte.
Surprisingly Petco had the nicest freshwater fish area and the only place I saw shrimp other then feeders.
Fishy Business I found rather disappointing to say the least.