This company sells new S-100 boards!

http://www.s100computers.com/Cards%20For%20Sale.htm

They have a Z-80 board. Lots of information about it here:

http://www.s100computers.com/My%20System%20Pages/Z80%20Board...

They also sell S-100 backplanes, serial boards, display boards, memory boards, and so on.

They have a Z80 single board computer too:

http://www.s100computers.com/My%20System%20Pages/Z80%20Board...

I have no connection to the company; I just think it's neat.