So sometime last year I was doing the main quest in Celestia and somehow got a permanent Stingray mount. I found this interesting because recently I've seen people on the forums saying there is no place anywhere in the game that you can get a free permanent mount. Now I know some mounts cost gold from the crown shop or I could've bought it with crowns, but I assure you if I was gonna buy a mount I would've bought a different one.
I have several permanent mounts that were drops. The mini mammoth drops from Boss on Jeweled Slopes in Polaris. Good luck to you.