In the City, you ought to be able to find some little old guy who repairs record players and radios and TVs -- check the Yellow Pages under Electronics Repair, or something like that. One of those old shops with a zillion dusty boxes and pieces of equipment sitting around. Call around and see if someone carries it. I presume you're talking about the one that fits over the spindle of the turntable and lets you stack a bunch of records and drops them one at a time (grinding the grooves of each one, of course....but there are no audiophiles for 45s, right?). If you don't need that, they also used to make little plastic inserts that fit into the hole of the 45 and turned it into a small hole. But they may be even harder to find!

You also might try a radio station, especially one that was a big Top 40 station back when. And there's always eBAy!

Aloha,
Mark

(I'm ashamed to admit it, but the first 45 I owned was "The Ballad of the Green Berets"! -- unless you count "The Mickey Mouse Club" and "Rusty in Orchestraville"!)