Hi Michelle,
Hobby stores are so hard to come by. I only get to one, and that's when I'm away on business. I've been having good luck with Amazon Prime. Stuff is at or below HS prices, and with Prime I get free shipping (in a manner of speaking) and delivery within a few days.
EDIT: so I looked at Testors website, and a few other forums (sub edit: there is a LOT of pretty horrible advice out there, like using lighter fluid and or Goof Off).
Testors says that their four enamel thinners, 1148, 1156, 1789 and 8824 are "interchangeable". With the caveat that 8824 is "diluted" for airbrush, whatever that means. I have used 1789 in the a/b with no issues.
I'll just repeat Morrison's Second Law: there's never enough time or money to do it right, but somehow there is to do it over. I've learned the hard way.
Sorry to preach, but better to be safe with that model.