Where can you buy a wood forearm for a Browning Magnum 12 gauge semiautomatic SS 49206 PP151?

Try checking on eBay for GUN PARTS. Sellers can not sell whole or complete weapons, but they can sell stocks, etc. Midwest Gun Works also sells Factory replacement wood. Brownell is another source. There are many other stock makers (that are not original Browning) on the internet - try the Midwest link below.