I've bought many shirts from cafepress www.cafepress.com

I'd go there and search on your fam. name and coat of arms and see if somebody's already loaded that graphic up...if so, pick a size and order your shirt.

If not, you can upload you're own graphics of the coat of arms/crest and order shirts, mugs, coasters, even thongs printed with it. Most are pretty nice quality shirts...they just print whatever you upload.