All of the exim web site content is available through rsync, and this is the recommended means for mirroring the web site content. A document describing rsync mirroring has been produced by Sunsite Denmark, and this gives good general information on rsync in general, where to obtain the software, as well as rsync for mirroring.
The rsync URL is rsync://ftp.exim.org/www
However the more normal means to quote the rsync path is ftp.exim.org::www
The rsync path for the ftp area is ftp.exim.org::ftp
Your httpd obviously needs to see the mirrored content. There are also some other tweaks - Apache aliases - which are needed. The paths that need aliasing are currently only the /ftp> path which either needs pointing to your ftp mirror, or redirecting to a reasonable mirror of the exim ftp site.
If and when the mailing list archives are put on line, these may also need handling in a special way.
In some small recognition of the ISPs and other organisations who donate the web site space, bandwidth and management, the web site has a brandable component - specifically the bottom left hand pane of the main window points to the branding/branding.html file. By aliasing this path you can tailor this to put a sponsors logo in place.
Assuming this is a public mirror then contact me about it and I will add a link from the main site. I can also get a www.country.exim.org link added to the DNS for you. You may also wish to send one message to the mailing list about this.