What t5's will work behind a 50 flathead

[35 coupe]

Had a t5 with mechanical speedo behind my 50 f1 and the syncros went bad after it was rebuilt twice. Because the parts are obsolete, what other t5's will work and where is the best place to buy them. I wanted to run my stock speedometer but now I don't care if I run an electronic one, as long as I get a good tranny. Thanks