Hi,

The most commonly used "food" cactus for tortoises is the Opuntia (prickly pear) group. I am not sure about the others in your mix. Depending upon where you live, you might be able to simply buy the pads by the pound in local a grocery store or produce market. Spineless pads are readily available here in the southeast where I live. It could take quite a long time to grow the cacti to an edible size from seeds.