I know Camp Kenan is not a great source but a video I have seen he went to someones house who raises Galapagos Tortoises. He had a sick tortoise that they found out gets very sick around once a year not eating can barely walk and they found it was endophytes in the hay causing the animal to get...
I had ordered some opuntia pads and instead of feeding I planted them in pots. They are now huge and the torts love it. They do grow very quickly and are easy to grow. I take them in for the winter and out during the summer. Just stick them in the dirt.
Go to a place like Tractor Supply and they have orchard grass pellets. Or to a place that sells hay for horses and you should be good. If your tortoise doesn't like the dry pellets or hay you can just add water a re hydrate them.