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Most libraries have access to at least one database where you can view the giving habits of foundations that work in your area of interest. These are called foundation directories or grant databases. Access to these databases are by dedicated subscription service so you usually have to search these databases using library computers rather than online. Smaller libraries keep these databases on reference CDs. The data is slightly older but you still get the addresses of people who have access to money and are interested in paying someone to do work that you would like to do.
Another is to monitor RFPs (requests for proposals) in your area of interest. Government agencies also post these independently when they are looking for people to do specific projects. Submit a proposal for any project you think you want to work on. You may have to form a company but that is not hard. One of the advantages is you get to choose your employer and your project.
I have two acquaintances who combined these two processes. They found a city that needed some invasive species work done. They used a grant database to locate a source of money, charged the city to write the grant, manage the project themselves and, hired local workers to do the work. Since the original work, the city has hired them to write a grant for a civil engineering project which they have hired a civil engineer to run. You can use a similar process in just about any field.
You might also set something like this up to run from inside a college or university. This is more hassle but you may get some teaching or research opportunities that would not be available if you worked in the private sector alone.