Where is the best place to get a Rochester Q-Jet?
Looking for a Q-Jet numbered 7029203.

Well, you could see if this is still available - http://www.lightningspeedshop.com/
(page down to the "Quadra-Jet Original Corvette Carburetors:" listing about 1/3 down the page for the info ... )

Other than that you just need to contact some of the carb. restorers and see if they have that core in their inventory they could build for you.
I did a quick check of some of mine and didn't see that code.

You might try Sean Murphy Inductions. He specializes in Quadrajets. Not sure of address, just Google him.

jw