I don't have any plain tribarrel cactus seeds. But I do have them in red, bright red, blue, bright blue, yellow, bright yellow, purple, bright purple, green, bright green, orange, and bright orange!
If you go to my Margrette's house just off the NE corner of Zento, stand on the steps (it's public) so you can see stuff, you'll notice a bunch of small red boxes locked down. They contain samples of plants in various colors. Check the box for tribarrel cactus and let me know which color(s) of seeds you want and we can use PM to make arrangements to pass along the seeds.