There are some 8" 5 lug axle shafts that will fit an 8" axle that originally had 6 lug(I'm pretty sure that is). 7.5" 5 lug axle shafts won't. And there are no 7.5" axle shafts with 6 lugs.
The only other way would be to drill new holes(5 lug pattern) in some 8" 6 lug axle shafts and install 5 lugs(instead of 6). That might be trickier than it sounds. I don't know...never done it.
Anyhow, I can't recall off hand what the details are. But if you search for yourself, you should be able to find all the details. The info's here somewhere...ol' what's his name
knows all about it(sorry guy, my memory's misfiring today for some reason). Maybe it'll come to me(or I'll get bored and look for it a bit myself).