The Linux Graphics mini-HOWTO, available at http://www.csn.net/~mjhammel/linux-graphics-howto.html and through the Linux Documentation Project, provides detailed information on where to get the software mentioned in this article, as well as other resources available on the net. Each tool listed has information on mailing lists, newsgroups, ftp sites and web pages, if applicable. I'll cover just a sampling of this information for some of the tools discussed so far:
XPaint and PMBPlus/NetPBM are both available from Sunsite, as are most of the Linux distributions currently available.
There is a companion web site to the Linux Graphics mini-HOWTO: the Unix Graphics Utilities page: http://www.csn.net/~mjhammel/povray/povray.html
This page is devoted to graphics tools for Unix systems in general, and not Linux exclusively. The main focus of this page is POV-Ray, and other 3D rendering tools, and the utilities that have been written to work with them.
There are a few Usenet newsgroups that would be of interest to Linux:
There are not many newsgroups devoted to the use of particular tools except for tools on other operating systems. I think this is a problem that the Linux user community will change as more users of Linux tools form their own user groups.