Lisa had a rim fail like that just by hitting some broken up pavement on the edge of Hellbender (or was it on the Dragon?)
I'd bet SOMEONE on the forum has a rear wheel laying around after upgrading to aftermarket wheels.... THAT I'd be more confident in buying than anything used, for the reasons already mentioned.
Yea, I'd post a WTB ad here and maybe start a thread on the Facebook page - SOMEONE has a good, used wheel laying around that you could trust to be good!