Ghostscript and GhostPDL releases from version 9.19 have been moved to GitHub hosting, and can be found here:
Ghostscript/GhostPDL GitHub release page
Releases 9.18 and earlier can be found here:
Ghostscript/GhostPDL Old Releases
The URW++ base 35 Postscript fonts releases can be found here:
jbig2dec releases can be found here: