JohnDo,
When you say it broke off, did it fall in? I'm assuming that you're talking about the plastic piece that's two concentric circles right?
If you push hard/deep enough, the center piece actually comes out. So it may be that you have a piece somewhere underneath the plastic.
Obviously you could ask the dealer, but I bet they charge $5 for ONE. I've never seen these type of fittings elsewhere, but Home Depot/Lowes might have something like this. Or you could go the auto route and try Pep Boys.
Good luck!