Nice piece. I know what you mean about the repro stuff - most of it is really gaudy. I have no idea if yours is the real thing or not, but I thought this might help:
Trade Axe and Tomahawk Collectors Association
(they probably have a good idea about the authenticity of your piece)
Here's a gunstock blade from their site that does look similar to yours though (scroll way down - 2nd to last at bottom of page):
killer gunstock style tomahawk spontoon trade blade