As for false gars, there are two in particular.
The Hujeta Gar, Ctenolucius Hujeta, which grows between 8-12". Also, the Needlenose Gar, Xenentodon Cancila. Not 100% sure on their size, I think they grow to about 12", maybe a bit smaller.
Spotted gars and florida gars are probably the two that will stay smallest. Spotted are very difficult to come across (unless you've gotten a hold of E_Americanus), so most likely your best bet would be florida. Still going to need a 125g minimum for a Florida.