In the past it has often been quite tricky finding out who are the wealthy donors giving substantial support to charities, universities, etc. However, it seems to be becoming easier, as donor recognition schemes become more popular.
If you check out the websites and annual reports of “competitors”, it can be surprising how much information is included on their biggest supporters. Sometimes they are listed as supporters, better still, as major supporters. If you are really lucky, there will be a giving band included, or even the amount they have given. This can apply to individuals, companies and grant-making trusts. Sometimes, one page tells you about what the various levels of support indicate, and another page lists those giving support at that level.
If you want to go beyond looking at the “competitors” that you know about, then creating an advanced search query with your favourite search engines can also provide useful results. Always use more than one search engine, if you have the time.