You can easily repurpose PS/2 or USB KVMs by replacing those connectors respectively with S-Video connectors. You can build an entire network of KVMs by replacing just the connectors on the KVM and terminal connections only, leaving any units in the middle of the setup stock.

Electronic switchboxen from TRENDNET are very inexpensive and come with all cables necessary. I'm standardizing on those and the OmniView series I've been using for 20 years.

There's another thread around here somewhere about KVMs.