I usually look on craigslist. I found a nice complete core for $300 that dropped a valve seat a couple months ago. The early models seem harder to find around here though. Here are some examples in my area.

https://york.craigslist.org/pts/d/05-hemi-engine/6468093926.html

https://washingtondc.craigslist.org/doc/pts/d/57-hemi-and-trans/6530601420.html

https://annapolis.craigslist.org/pts/d/2010-dodge-ram-2500-parts/6496707097.html