Your best bet is probably craigslist. Just look for postings with crt monitors and search make/model for a manual and perhaps some reviews. Make sure it can do at least >~110hz (crts don't usually hit 120 on the mark many are like 116 or 118hz). Make sure also to check the driver situation as some monitors are weird with windows 7 and you have to pull some voodoo to make them to operate at their max refresh rates, but that's sort of unusual.
Most crts you will find only go over 100hz at 1024x768 or lower, but that really shouldn't be a problem since tf2 is completely fine at low resolutions.
You should be able to get one at free or near free unless it is especially nice because people just want to get the heavy, huge, and outdated object out of their homes.