You've already started it. 
Just modify this post to say you will accept emails with club information, and then catalog it in the first post.
Done. No special forum, categories, etc needed.
Of course, it does mean significant work for you to go through all the emails people send you and organize it into a meaningful form. A simple Excel file with filters to break down by state would seem to be a valid starting point.
As to the demographic area of Philly and the surrounding area anywhere close in NJ, it's surprisingly sparse in terms of clubs with a home base layout type situation to the best of my knowledge.
(NJ Highrailers doesn't count as "close" to Philly, since it's around a 2 hour + drive for most people in this area - though it is of course AWESOME! I've never been to North Penn, but it does sound nice as well.)
The key to ALL clubs with large permanent layouts is finding a large enough space available for an amount of money that can be considered Hobby spending by the members. I don't have any answers for that.
-Dave
