What you want to do, is get a few "hubs" (90's era networking equipment)
that have a mix of AUI, BNC, and 10BaseT connectors, and then cable the hub up to your
more modern 100BaseT and faster switches.
A hub with 4 to 8 10BaseT + a BNC was a common configuration on consumer-grade stuff in
the 90's, and it was on the more industrial rack-mount networking solutions too (and
there you'll often get an AUI as well).
I have only made small efforts searching out new-manufacture hubs with BNC's but as
far as I can tell, they simply aren't being made anymore. Everything new is a switch
today. Keeping a few hubs for protocol sniffing etc. is still handy.
BlackBox etc. still sell new "Media Converters" with a 10Base2 on one end and a
10BaseT on the other end but the prices are heinous (e.g. $225:
http://www.blackbox.com/Store/Detail.aspx/FlexPoint-10BASE-T-to-BNC-Media-C…
). I give them credit for still selling a networking technology that isn't the latest
and greatest.
Tim.