The hardware store may have them.
With that said, I've had a less extreme but similar situation with a small female the day I got her (barely socialized and obviously would not come when called, etc.). She fled under the cabinets in the bathroom (I found out there was a tiny hole underneath ... bad construction I guess). Well in a panic, I constructed a "trap" of sorts. Basically a hamster cage top (the wire part), held up by a chew stick attached to a piece of dental floss attached to a lab block in the middle of the space under the wire top and I also hung a small bell.
I know it sounds like right out of a cartoon but what can I say ... first rat, I didn't know what to do and rattie girls was NOT coming out. Well lo and behold after a couple of hours I heard the bell. The little gall had come out and tried to help herself to the lab block, pulling the string and chew stick which made the wire top fall down (around her not on her obviously) and she was trapped. She was pretty scared but I couldn't just leave her in there.
Until you get a proper trap you can try something like that. And for the trap I read somewhere that cooked eggs are a favourite among city rats so you may want to try that. Whatever you put, make it something that can be smelled from far away.
You may also want to reduce the noise in the area where she disappeared and keep the lights dimmer. It may make it seem less scary. Any used bedding you may have could also help ... I'd put it in the trap as well so it will smell familiar ... or heck leave the trap in the cage with your other rats (unarmed obviously) so they can scent mark and pee all over it. Again. Who knows, it might make the "new" thing seem less scary.