Hmm.
Not really aware of any Kindle e-ink font repositories. Perhaps someone else will know. Or you could start one here. I believe that Amazon added the custom font feature in mid-2018 (fw 5.9.6-ish).
Before that we relied on work by NiLuJe and ixtab,
et al to customize fonts
e.g.
FW 5.3.x - 5.7.x Fonts Hack
Notwithstanding the thread title, the above should work pretty well through 5.9.7 and perhaps with newer fw as well
Google Fonts has about 1,000 free, open source fonts. Albeit not specifically geared towards e-ink readers. And a quick Google search pulled up the resources below for a start:
Best places to find free fonts (Design Shack)
Best fonts for Kindle (Reddit)
Top 10 custom fonts for kindle (Epubor)