^^^What he said
I bought an LQ9 back in 2010 from M&M Auto Parts (
http://mmauto.com/). I found them as well as a bunch of other yards on car-part.com. After lengthy research, many phone calls and word-of-mouth reviews, I felt they were a reputable source. It turns out they were the yard that sold me a 4.3 for my S10 a few years prior. That motor was everything they said it was and so was the LQ9. The amount and type of business they do pretty much prevents them from even having the time to lie about their stuff- numbers can be traced, info looked up, etc. They seem to be growing a lot and just announced a late model division. I'd comfortably buy from them again.
Also, I'd recommend one from an Escalade because there's much less chance of it being beat on than if it had come from a Silverado SS. Mine was a complete 31K-mile pullout with all accessories, shipped for around $2,200