I have the M1919 from Marstar in .308. It's non restricted, and if you use origional WW2 type belts, there is no mag/belt capacity restrictions. Pretty heavy, mind you, but think of it as a bonus work out.
As a more reasonable alternative, but not S/A, you could find an Enfield .308 conversion. Best examples are the DCRA conversion no4mk1 or 2s, or else the Ishapore no2As are well regarded. And 10 round mags go with both of these.