try putting a post in my classifieds site,
PerformanceTrader.net, here's the direct link to the engine section ->
link
Also, try
LS1tech.com,
Lt1tech.com, and my buddy Chris's site
Ls1lt1.com also, lots of good stuff up for sale there.
don't forget ebay and autotrader also.
Really shouldn't be too hard to find a used LS1 or LT1