The field control hardware can be bought here.
If you just want to run a small scrimmage, you can get away with not using any field control hardware, and jut trusting everyone to start their autonomous programs and start and stop driving at the right times. Or, connect all 4 controllers to a competition switch, and have someone flip the switches manually at the right times.
Tournament manager is a fairly complicated piece of software, but not too hard to use with a bit of practice. I made some introductory videos a while back going over how to set up and run an example tournament.