here's a couple of places to try.....................
www.hemmings.com
http://www.vettehound.com/geo/classifieds.php
I sold my 66 back in January, prices continue to rise on midyears especially on matching numbers cars, theres lots to be careful of and there are many fakes out there. If your going to invest in a matching numbers car be sure to be thorough in researching the history as restamping engines now a days appears to be a common practice. Not only do you need to check stamping numbers but you need to check casting numbers to ensure that the stamping numbers are legit.