Mosa Tek Saddle like other armor pieces and/or saddles can have different rarities. Atleast on Steam Ark the only way to find these is in Extinction through high level OSDs or maybe titans if your lucky.

If you find a blueprint there is a possibility you cannot craft it because the Tek Replicator only has so many slots for the insane amount of metal it costs. This is why i recommend playing with a stack mod on Steam or just on ASA in general.

The Mosa Tek Saddle is a little more niche than the others but still has its uses. Raiding Underwater Bases and using the Tek Saddle Dino + Soaker strat still works, A good Mosasaur with the Tek Saddle is possibly one of the best ways to grind black pearls on Ragnorak by sniping the Tuso Overspawns. I’d recommend doing this over killing eurypterids if you play with rather low gathering rates. Could use a few of these guys to take on Moeder pretty good as well,

I personally love Tek Saddles, but the Mosa’s may be the least used in the game, namely because the water is not that popular or necessary in almost every map.