Try e-gunparts.com or MidWest Gun Works.
gun shop, gun show, pawn shop, want ad.
Check the receiver, barrel, under the forearm
ebay, gunbroker, Brownells, Midwest gun works - all on line
Try MidWest Gun Works
barrel, butt, receiver, under forearm.
Contact Browning.
Check Browning's website.
Try Calbelas Shooting Catalog, that's where I got my stock and forarm for my auto 5 light twelve. Why they named it the light 12 is beyond me.
usually the stock is behind and the forearm is in front of the receiver.
Try MidWest Gun works or egunparts
Try Mid West Gun Works.
You can find them on eBay periodically and at Gunbroker.com. also Midwest at the related link listed below.