How do you get the trex in fossil fighters

there are 3 ways, you can either dig for him in Parchment Desert, one of the two places you can get from finishing the main story line, buy him in the shop, or get a friend to trade him to you.
finding him at the store is the hardest and getting him from a friend the easiest, it's a rare fossil so don't get your hopes up, but like most fossils, once you find it it's every-where!