I had never heard of UV photography, how cool...
Anyhow, you can find them.
http://www.adorama.com/1/1/168553-peca-62mm-9-filter-kit-fk62.html has a UV filter in the kit, a Wratten 18A.
http://www.bhphotovideo.com/c/product/8219-REG/B_W_65011796_77mm_UV_Black.html ($200) is a B+W 403 filter.
I found this with good google-fu.
Take the filter types (Kodak Wratten 18A, B+W 403, Hoya U-340, Baader U-Filter and Kenko U-360) and put them into google along with a common thread size, say 77mm. And start clicking on the hits.
Or you can build your own filter, I just found this link. http://www.instructables.com/id/Photography-in-the-Ultraviolet-spectrum/ basically they take an incandescent black light, break it, and rig up something to put the glass over your camera lens. Might be tough to get a piece large enough for a big DSLR lens though.
And show us what you shoot!