When I was looking I checked eBay and craigslist. Another place would be the forums on plowsite.com. (I think that's the place) Mounts were going for 200 up when I was looking. I'm in Iowa.
Otherwise you might be able to make another mount fit your truck, but I would only be doing that out of necessity. Not hard, but could be fussy work to get it all working right and strong.