something ate my paint; best place for touch up paint

i just started washing my car, which is the dirtiest it has ever been sinced i owned it, and there was some white stuff on the bumper. at first glance i thought it was bird poop, so when i went after it with the sponge, my paint came up. apparently not bird poop. so now there are some spots on my rear bumper where it is just the yellow bumper itself. so my question is, where is the best place to get some touch up paint (black) that will match decently well? in days before when i would go to the autoparts store they would have a book, that you could look up your paint code and then get the correct stuff. but last time i went there they did not have anything like that.
any input?
Thanks

The Green GT said:

I know there is a website that will actually mix you a spary can of any color code. But I dont remember the site.

Maybe someone else will.

And black wont touch up very well, so dont expect a miracle.

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yea, i dont have my hopes up very high, but i figure black will be better then yellow. also i kind of want like the kind you brush on. i think that that would be better suited for these spots.