Any of thr axel manufactures can supply you with good hp 28 spline axels that will fit your 8" rear. When you get a 9" you can use the same axels. 28 spline are just fine on a street car and hardend axels will hold up ok under some race conditions
Cool.
However axles are not considered the weak point in 8" rears.
They use 28 spline axles as the 9".
28 splines are known for breaking in 9" rears, since they are the weakest link in a 9".
The carrier and gear case are the weak link in 8" rears.
I have broken a few. Even broke the gears themselves in one.
Could have been due to a pinion support failure though.
I never checked... Just got another chunk and kept going as before.
Dave