You can buy the B.B.I. - Nano Enhanced B-12 Tanning Acid from Pharmacy and Chemistry Components Terminal. You can find Bronto hides all over Rubi-ka (and due to some lost Bronto Mamas even in Elysium). They tend to drop from Bronto mobs and are also found in mission chests. This was good news, bad one is that it's another type of tradeskills that requires a Mass Relocating Robot (Shape Soft Armor). It is not sold in shops, check our Mass Relocating Robots guide to learn how to get it.
Treating the hides
You will need to treat the hides before making the armor: