Cavalry Manufacturing has been working on a new lower for the SCAR MK17S for some time now. I was recently given a prototype to test with my MK17S.
The upper on the SCAR is the regulated serial numbered part, so the lower is basically a trigger pack/magwell module. The Cavalry Manufacturing unit is machined from aluminum billet and accepts the parts out of your existing SCAR MK17S lower.
I will be testing a production unit in the future.
Contact Cavalry Manufacturing at http://www.CavalryManufacturing.com