Do you need a real nice one, or just one that works? I assume you also need the gasket, bolts, clamp. etc.?
This guy has a new one in stock (it isn't cheap):
http://www.hondarestoration.com/nosResu ... MR175-1977... and this guy may be willing to pull his off the motor and sell it separately; I've done this several times with CR125 manifolds:
http://cgi.ebay.com/ebaymotors/Honda-CO ... 3efff983a4I'm surprised there aren't any on eBay. Over the past couple of years I must have seen 20 or more for sale there, either separately or with a carb or cylinder attached.
I may have one in my parts box, but I believe it's been repaired.
Ray