That’s a good, non-trivial question. There are various lists / directories of venture capital funds, e.g. https://en.wikipedia.org/wiki/List_of_venture_capital_firms.
But if you’re looking for angels, that’s much harder. I don’t know of a single, comprehensive list of angels. However, AngelList (ironically named in this contest) shows many companies and who invested in what: https://angel.co/. So that’s one way to explore, and maybe someone has built a directory on top of that.
Another approach that’s worth trying is looking for other companies in your space, and who invested in them. This is usually available in press releases and such. While some of these investors won’t be able to invest, they can intro you to others, give you good feedback, etc.
I hope this helps!