I read in the Ranger forum that there's a Detroit Tru-trac available for the 7.5. The design is similar to the Torson l/s now standard in the new Ranger FX4 Level II. No clutch pack to wear out and the performance is said to be excellent. Don't know who might be able to order one(UAP?), but online ordering and shipping from the states is pretty easy. Check out the FTE sponsors as they usually offer discounts to FTE members.
As for a conventional L/s, a good local boneyard should be able to tell you what applications had a 7.5 l/s and whether they have one in inventory, unfortunately they'll likely tell you that you have to purchase the whole rear end at which point you may as well upgrade to an 8.8. And you'll likely have to replace the clutch pack as they degrade with use.

Good luck
Fred