You can use pretty much any 35mm format interchangeable lens ever made on an A7. (There are some exceptions, of course…Zeiss Contaflex lenses are currently a no-go.) Canon FD is no problem, just get an FD-to-FE/NEX adapter. Novoflex makes one, and I've had good luck with their adapters on various cameras including an A7r. There are less expensive options too, maybe more appropriate for a rig that'll be beaten up.
-Dave-