Welcome to the addiction of Pinball!
OK well here are some links to get you going. Pinball is totally cool! I wish I had more of them. They do take some maintenance and upkeep.
On google groups go to rec.games.pinball
That is probably the best message board/forum. There are some stinkers on that board, but there are also a lot of really cool helpful people.
Next a great resource is www.ipdb.org
The Internet pinball database. The machine you are looking for is the Stern NFL which you could then buy a Bears backglass translite. They have a pic of it on there.
Now for purchasing one. For your 1st, I might recommend a local dealer that can get it setup for your and show you the ropes etc. If you are a total DIY kinda guy, check out http://marvin3m.com/top/
There are some really great DVDs that show restoration etc. There is a link at the bottom for Clay's info. and repair guides.
OK if you don't go for the local dealer or the dealer doesn't have what you want, the 5 top ways I find something are:
they have a great classifieds section
4) put a WTB post on rec.games.pinball
5) Go to a know good out of state dealer e.g. www.actionpinball.com
A dealer will cost more especially if he has shopped out (cleaned, repaired, new rubber, bulbs etc.) the machine or done restoration. There are operators that you can go to, but I don't recommend that if you are just getting into it.
Let me know if you have any other questions!