It looks like someone has already done this.  The mirror FTP site at
ftp://ftp.nuri.net/pub/FreeISO/netbsd/ has this:

Current directory is /pub/FreeISO/netbsd

Up to higher level directory
CHECKSUM.MD5                    56 bytes Thu Sep 09 04:20:00 1999 
NetBSD-1.4.iso              664170 Kb    Sun May 16 09:34:00 1999 

It would be nice if whoever built this put a readme there...



____________________Reply Separator____________________
Subject:    ISO images repository
Author: Marc Baudoin <babafou@babafou.eu.org>
Date:       9/22/1999 11:32 AM

Seen on Freshmeat this morning:

   <URL:http://freeiso.linuxsw.net/>

   FreeISO Archive Project is to collect freely distributed
   ISO9660, CDROM Image.

They already have images for FreeBSD and various Linux
distributions.

Any interest in making NetBSD images?  It should be pretty easy
to do from one of the official FTP sites.  As an example, the
size of an i386 distribution, plus sources, plus binary packages,
is approximately 420 Mb.  Maybe making such an image for each
supported architecture makes sense.  The rest of the image could
be partially filled with a copy of the WWW site and whatever
stuff could be gathered.