CGZ has been recommending Peyer's organ works for a few years now, and I wasn't able to find any of his music online.

I did a lot of looking, and kept coming up empty. Finally, I successfully obtained a score from an academic music library, and (through a collaboration with Pierre Gouin, IMSLP engraver extraordinaire) we are able to make Peyer's organ works accessible to everyone. There are only a few pages of music engraved currently, but there should be more to come shortly.

If you'd like to check it out at IMSLP, here is the URL: https://imslp.org/wiki/Præludium_&_Fuga_primi_toni_(Peyer%2C_Johann_Baptist)