I had purchased a 3/4 ton rear end out of a 51 Chev which came with 16' split rims. I had to send them to a wheel shop to mount 15"x8" rims on the original centers. I have never seen 15" split rims, but that doesn't mean that they don't exist as a stock GM part.
I'll have a look in my parts book to see if they are listed. This is the Canadian Chev book, so there may be differences.
Bob