Places to find singlets?

Hey all, I'm interested in buying singlets, but I don't know my sizing and want to try some on (I'm right on the line between sizes, and it seems not all brands are the same). I'm having trouble finding stores that carry them in my area. Ideas...? I know I could get them online, but sizing...

Fabric stretches so you will have some flexibility. Rare to find sporting goods stores with singlets. I'm 5'8" 140 lbs and go with an adult small in most brands like Asics, Adidas, Nike, Aussiebum, N2N