Winchester Model 70 (LA) or FN Police SPR (LA) Stealth Detachable Mag Bottom Metal at Pacific Tool and Gauge
pacifictoolandgauge.com
It's going to be tough to find bottom metal that accepts AICS magazines on a Winchester, but I believe it's doable.
I don't enough experience to provide a lot of info, though.
Your best bet is to do some searching here.