Who knows where and if you can donate?

I don't think that's how that works. You can't just fertilize an egg and create an zygote for the purpose of creating stem cells, that's just unethical. Plus I'm pretty sure stem cells can be taken from the human body, not from fetuses.
If you want to help people, donate your bone marrow.

I do know you can, however, donate your eggs for a pretty penny. Some sperm banks exist as well that will pay men for their genetic material, usually only if they have certain qualifications (usually a college degree, or doctorate). I think you can also donate stem cells in a baby's umbilical chord, should you choose to have one someday.
As far as specific places that do this? I'd say just google it.