Wyeast sells several varieties of brett yeast and other "bugs" used in brewing.
Brettanomyces Bruxellensis is Wyeast 5112
Wyeast 3278 Lambic Blend and Wyeast 3763 Roselare Blend are good blends of ale yeast and "bugs" for brewing sour styles.
Whitelabs also makes individual cultures and blends for the same purpose.
White Labs "Bugs"