Open-source maintainers, how do you search for sponsors?

I'm an open-source maintainer of a moderately popular developer tool. While I got sponsors from time to time, I would like to find more to sustain myself and dedicate more time to the project. I tried to contact companies sponsoring other open-source projects through Twitter or by email but got no response most of the time. I don't expect instant success, and I know that I am pretty average when it comes to marketing/sales. But still, I would be curious to hear from other open-source maintainers and their strategies, if any.