might have some luck with this craigslist search engine... allofcraigs.com.
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searches through all the local CL sites nationally for your specified item... i tried 'kayaks' (lots of results) 'creekboats' (some) 'kayaks montana'
(it really works for more readily available items....try typing in 4wd Tacoma....you'll find some cool trucks instantly)
try being very specific (i.e. LL stomper 90, Jackson Kayak Karma Large) then work back from there....
Also worth a shot....my local boating store 5hours north.... they always have something going on. a used/demo fleet and trade ins. especially with paddle fest coming up, there will be loads of new used boats all summer.
Colorado Kayak Supply - Kayaks, Accessories, Gear, SUP, Standup Paddle