The bottom of the popt manpage says:
popt.ps is a Postscript version of the above cited book
chapter. It can be found in the source archive for popt
available at: ftp://ftp.redhat.com/pub/redhat/code/popt
This directory does not exist on the ftp server anymore. popt.ps also
doesn't seem to be on ftp.rpm.org, unless you look in the popt tarball.
URL changed to ftp://ftp.rpm.org/pub/rpm in the popt.3 man page in CVS, will
be in popt-1.6.3.