There is an riaforge.org, which has some stuff, but it sounds like you
are looking for the adobe exchange (http://www.adobe.com/cfusion/exchange/
). There is a section for each product, air, flex, etc...
flex section: http://www.adobe.com/cfusion/exchange/index.cfm?event=productHome&exc=15&loc=en_us
air section: http://www.adobe.com/cfusion/exchange/index.cfm?event=productHome&exc=24&loc=en_us
Hope that helps,
Daniel