Sorry, I can't help you with the NY music stores. I'm not sure which magazine you're refering to, I subscribe to Vintage Guitar and there are some classified ads in it, but I think the best place to find a used G&L L-2000 is online. eBay has several for sale right now, and the classifieds here at talkbass have had a few over the last several months. Craigslist is usually another, but I have seen very few L-2000's for sale in my area (Texas).
Hope this helps. I'm in the market for a used one right now, I have a L-2500 and it's fantastic, it really punches through the mix, but I'd like to have an older 4-string as well.
Also, G&L has a nice forum
http://www.guitarsbyleo.com/.