Are there any?

While it's on the small side, it will still take you a few hours to get from north to south in NJ, so you might want to disclose your area first.

Every shop will probably have a used bike or two. Finding them, however, will be difficult unless you visit lots of shops frequently.

North Jersey. I'm lookin more for older road bikes, early 90s to 70s decent quality bikes I guess. Nothing museum quality just something to get around on.

Have you checked craigslist?

Yes

check out Congers Bike Shop in Rockland Co, NY. I hear they do a fairly extensive 2nd hand buisness.

The prices of used bikes at the LBS will make CL listings look like a bargain. My local Marty's has hatched this "Eco-Chic Bicycle Boutique" program where the convert low end bikes into hack job fixies or single speeds and sell them at ridiculous prices. I believe they are asking $325 each for these two monstrosities:

https://martysreliable.com/page.cfm?PageID=691


https://martysreliable.com/page.cfm?PageID=692

Now that I think about it, there is one shop in Washington Township (Warren County) that I seem to remember carrying a few used bikes. I can't remember the prices though. It was definitely an old-timey bike shop, with very limited hours (couple times I went there, seems the retirement aged proprietor was the only one working there). If you're anywhere close, might be worth checking out.

https://www.mccormicksbicycle.com/history.php

What size frame are you searching for, by the way? Some of us have way too many bikes.

Oh yeah, Whippany Cycle always has a few pretty nice used bikes hanging from their ceiling. Unpretentious bike shop with a very friendly and helpful staff.

https://whippanycycle.com/

This isn't exactly in North Jersey, but... When I was looking for a bike a few weeks ago, I stopped by this place called Padi's Pedal Power on Fischer Blvd in Toms River that had some used bikes in front of the store. Maybe you could call to see if they have anything you might be looking for before you make a trip down there since you're in North Jersey. Their website with their info is https://www.padispedalpower.com