I am faced with trying to install a frameless shower door on glass block. The problem is that with the weight of the 3/8" door and the spacing of the hinges;it is not feasible to anchor the hinges into the grout joints. Any suggestions?

I would try calling a local glass shop , the type that cuts mirrors , table tops ,etc. These type shops usually have techs who are used to going into the field and installing on site.
It may be possible to drill the block in place and set an anchor in epoxy.
Be prepared to replace block(s) due to cracking. The glass mechanics are unlikely to be able to guarantee results. Another approach is to find matching block , very precisely calculate hole locations. Drill correct holes in a shop ( where it is easier and more predictable) , set these prepared blocks, hang door.