At least the following anonymous ftp sites carry Linux.
Some sites mirror other sites.
At least sunsite.unc.edu and ftp.informatik.tu-muenchen.de offer ftpmail services. The distributions have grown to hundreds of MBs of Linux software, and downloading that over even a 28.8 modem takes a long time. If you purchase an archive, you will almost always get several different distributions to choose from, but usually support is not included. When you purchase a distribution directly from the vendor, you usually only get one distribution, but you usually get some form of support, usually installation support. There are many BBS's that have Linux files.