First off, welcome to Wild Texas! This is a pretty great site. Hope we can help you with anything you need.
Can't help alot with used canoes. I know that they can be a bit tough to find in good condition and at a fair price. Often the best way to find one is through "word of mouth" and then you have to jump fast. Wishing you luck in your search.
As far as carrying it on a pick-up with a PU in tow, that I can help with. Site below will take you to my PhotoCenter and will show you how we carry our 'yaks. Works real well for us with no problems at all. Have a look:
'Yaks and How We carry Them
There is at least one member over at RV.NET that is using this system to carry a canoe so I know it will work. Only difference between our set-ups is his bar and yoke is made by Thule and our's is Yakama. Both are very good names so it really makes little difference which brand you choose.
Hope this gives you the info you need. Feel free to ask any questions you want. Again, welcome to Wild Texas and, as always,
Happy Camping!
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Turn Key, DW & Tilly, The Camping Boston Terrier
'03 Chevy 2500HD, 4X4, X-Cab, Long Bed
'04 K-Z "Durango", 275RK ("Sunday Haus II")
Twin Kayaks, "The Ride" by Wilderness Systems
North Central Texas, Where The West Begins!