You can contact ButtonMashers, the crafty, geeky Montreal couple who made these t-shirts depicting Mario in all his Che Guevara goodness, and see if they're going to make any Onesie-brand bodysuits from Gerber, or maybe some other, less-well-branded bodysuits of some kind for babies.
Or you could just get one for yourself, while supplies last.
Mario-Che T-shirt in Yellow or Blue, $15+$5s/h at etsy.com, the marketplace for handmade stuff [etsy.com via boingboing]
http://mariorevolucion.ytmnd.com/
i think the Mario Che I made is considerably better.
[it's certainly more easily grabbed and turned into a onesie. heads up, though, the 8-bit music starts playing immediately. -ed.]