Yep, one by Czech Technical University:

https://www.ciirc.cvut.cz/covid-2/

https://www.rp95.cz/en/

And most rencently, after the 3D printed protoypes turned ot to work very well, an automated assembly line was put togehter in record time:

https://www.ciirc.cvut.cz/seriova-vyroba-ceske-masky-s-nejvy...

The other major technical university - Brno Uiversity of Technology - also developped a 3D printable face mask design:

https://www.vutbr.cz/en/mask

https://www.vutbr.cz/en/but/news-f19528/covid-19-protection-...

In comparion to the mask above, this is a 100% DIY design that one can assemble with common hashold items and a 3D printer.

Yes, search on Montana Mask. The 3D files are available and you could print them at home. Part of the mask is the filter holder which you can stuff with N1900 or greater furnace filters, vacuum cleaner HEPA bags or whatever. Edit- sorry, it's not quite like the P100, the filter holder is a rectangle in the center of the mask as opposed to the mask in the article that has two filter holders.

Not unless you have a material that conforms nicely to a face. But you can still buy face pieces. The filters are what are hard to get.