Bouldersmith

Sounds like the swivel loops you have were to be used for sling ends with buckle fastenings rather than the pigsking thong ends, the latter usually fitted to a round eye only, a number of older guns and rifles had narrow loops fitted, often sewn to the end of a wide 2-3" canvas sling, it should be no problem to have such a sling run up, possibly by one of the outfits listed in the previous mails, alternatively you may try Trader Keiths as they often list safari type slings and cartridge belts in canvas webbing.