If you like high quality vector color ornaments have a look to the aridi collection. http://www.aridi.com

If you like ornament fonts try http://www.myfonts.com/search?search%5Btext%5D=ornaments

—astype.de—

Underware’s Sauna has some cool dingbats
http://www.underware.nl/site2/index.php3?id1=sauna&id2=detailsdingbats

I hate to be a downer, but you will need to read the EULA of any dingbat/image font very closely before you use it for t-shirt designs. Many foundaries do not allow their dingbat/image fonts to be used as a sole element in a design such a t-shirt of logo.

I once had a designer use a glyph, capital D, from one of my fonts, as a corporate logo.
I was fine with that, but pointed out that the client wouldn’t be able to copyright or trademark their own logo. The same holds true for ornaments/dinbats, I would imagine.