Vintage stock, second gen 3-prong can be repro if it matches Colt grey. 
The Innovative Industries 3 prong flash suppressors come in black oxide or grey phosphate. > https://www.innovativeindustriesllc.com/collections/flash-hiders-compensators/products/flash-hider-early-3-prong
It’s the best reproduction that I’ve seen.
USGI D type stock
http://shop.ar15sport.ihoststores.com/productinfo_v3.aspx?productid=RETBS-1
Brownells repro D type stock
https://www.brownells.com/rifle-parts/stock-parts/buttstocks/ar-15-retro-buttstocks-prod109339.aspx
3-prong FH
http://shop.ar15sport.ihoststores.com/productinfo_v3.aspx?productid=ARPART-107
split washer
http://shop.ar15sport.ihoststores.com/productinfo_v3.aspx?productid=ARPART-71
3-prong FH installation tool
http://shop.ar15sport.ihoststores.com/productinfo_v3.aspx?productid=TOOL-3P
Yikes, I thought the stocks were cheaper than that, I’ve seen full furniture sets for $75. The Brownells are supposed to be really bad when it comes to replicating the feel.
Here is another I found. It states that it is refurbished. It is much cheaper.
http://www.e-sarcoinc.com/m16originalgibuttstockwotrapdoorrefurbish.aspx
Up until about 3 years ago, I was buying D type stocks for $15-$25. Those days are pretty much gone as are most of the stocks.