I've come across testers in a couple place. Newark for sure, back in the day you'd pull up looking for a certain stamp, like "who got the blue espn's" (which was, by the way the most FIRE shit I've ever had in over 20 years of h usage), and the they'd be like, " naw I don't have those but I got such and such, here try one out".
Also the LES back in the late 90's was a place you could get testers, usually early in the am though.
And I've also gotten testers on the west side of Chicago a few times. Twice I was followed from the spot, once they followed me far as hell, all the way down to the spot by the airport I like to fix and then go grab a couple gyro's, to offer up like 3 bags of their stuff for me to try, along with their number. That one turned into a like year and a half business relationship with this cool ass cat who I'd call on my way into the city, and he'd meet me by the freeway/airport so that I didn't have to go into the hood. Miss that dude.