A source of useful dimensions is http://www.simpit.de/a320dim/page_01.htm
You can find panels and many other parts on www.flightdecksolutions.com
Many other useful interface cards etc on http://www.opencockpits.com/
Jeehell software https://jeehell.org/forum/index.php

Skalarki hardware http://www. skalarki -electronics.eu

From those sites you will find links to many more sites.

Flight DeckProjectA320 MathiasWohlrab http://www.fdpa320.com/
Darren Sugden's A320 - just down the road http://www.sugden.karoo.net/