Any of the aftermarket axle manufacturers can make these. Or make em for whatever bolt pattern you desire. 28 spline 8" axles are the same units used in 9" rears.
You can have anything custom made! I was looking for ready made inexpensive 8" ford 60's Mustang or mid 70's Granada axles to buy. Press on my bearing retainers and Bob's my uncle! Thanks Wart .........ahh I mean it'samustangII