There is a selection of the 1970 version on eBay
Revell '70
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3149959761&category=2581
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150305261&category=2585
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150512982&category=2581
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150838727&category=2581
with AMT '70 Challenger R/T
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150551706&category=2582
with Revell '71 GTX
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150561607&category=2582
There seems to be some variation on price.
There is a 1971 MPC Roadrunner
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150828705&category=2585
but seeing as there is another that has reached $51 (plus shipping) then that could get expensive.
If you are after some spare parts (it does include an MPC Roadrunner - possibly the '71?) this is worth a look:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3150714410&category=2585