Anyone know where I can get a virtual boy shirt?

If you want an original T-shirt (which tend to be quite expensive for a shirt, just to warn you), you have to wait for one to come up on eBay or another website that sells VB stuff, or happen to know someone who worked for Nintendo back when they were given out. I got mine through eBay.

This site also sells shirts, see the link below:
http://www.vr32.de/modules/about/?s

If none of those options fit your tastes, you could make one yourself or have a friend make one for you and buy it through a custom shirt website, such as CafePress.