Here are a few that I know of:

- https://careercenter.aiaa.org/

- https://www.cfd-online.com/Jobs/

- https://www.clearancejobs.com/

- https://www.fusionenergybase.com/jobs

- https://jobs.hpcwire.com/index.cfm

- https://www.higheredjobs.com/

Some of these are extremely niche, but for the right people, you could strike gold.

I came across this a few weeks ago on HN:

https://www.jobsearchdb.com

Check out https://jobboardsearch.com a directory of job boards

I know one for high finance (private equity, M&A etc..) mainly focused on France / Europe with some data in the US : hundreds-ai.com

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