Among a lot of other militaria, including sporrans, kilts, trews, doublets, etc..., this ebay vendor currently has about a half a dozen original military archer green wool Inverness piper's capes in various sizes up to 48-50 chest. They are not cheap, but if you are into authenticity and military surplus quality you might look into this guy's ebay store:

http://shop.ebay.com/bugpiper/m.html....c0.m14&_pgn=1