FWIW, last I knew things were a bit painful with most of the US-based sites and non-US contributors drawing from them. (And things generally get pretty horribly mirky for me with UK tax rules.)

Maybe you want to try https://codesponsor.io/

I think this may be a great place: https://opencollective.com/

it better to put on the front page that this project need sponsor.

Tidelift says:

This project has no income available yet.

You can help point potential subscribers to us and be ready to accept funding the second it is available.

https://tidelift.com/lifter/search/pypi/html5lib

The Linux Foundation has launched CommunityBridge to help with funding, security and mentoring.

• https://devclass.com/2019/03/14/linux-foundation-offers-devs-and-project-maintainers-help-with-money-mentoring-and-security/
• https://communitybridge.org/

Currently Tidelift says:

Income Estimate: $224.87/month
This project is eligible for a share of fees paid by Tidelift subscribers.

https://tidelift.com/lifter/search/pypi/html5lib

So you can start grabbing the income, aka become a lifter.

Who would actually be the maintainer if there were funding available? Are any of the current maintainers seeking funding?

@twm As of next month I should have the time to actually work on html5lib, provided I'm paid for it.

We'd love to have one or more maintainer join Tidelift to receive funding for html5lib!! Are there any questions I could answer for you?

GitHub now provides a sponsor button that can be linked to tidelift?

GitHub blog post : https://github.blog/2019-05-23-announcing-github-sponsors-a-new-way-to-contribute-to-open-source/
https://tidelift.com/subscription/how-to-connect-tidelift-with-github