i have seeds for Thelocactus setispinus(i have hundreds of these) Echinocactus texensis(horse crippler) and mammillaria prolifera(i think it looks just like it) and the plain texas prickly pear cactus
You might try the Plant trading forum here: http://www.botanicalgarden.ubc.ca/forums/forumdisplay.php?f=133 (Apologies if you've already tried this....)