A new etsy shop opened yesterday called Sashapotamus, selling adorable screen printed t-shirts for Sasha/Gregor and onesies for Sasha Babies. They're eco-friendly too, with low-impact vegetable dyes and solvent free ink. I must confess I've done quite a bit of shopping there already. I've added it to my LINKS section in the left sidebar for future reference.
And if you're interested in t-shirts for babies/children with many of the same screenprints, check out Jackapotamus. You just may see pictures of Boo and her Sashas sporting matching tops in the future. :-)