game_* entities certainly weren't intended to be used in TFC because they're missing from tfc15f.fgd (which you should be using). So I'm not sure whether you can or should try to get them to work. Maybe someone with a little more TFC mapping experience can help out.
Map-based screen messages aren't, in general, part of the TFC experience anyway.
BTW, the TFC entity list is not directly linked (hint, hint) but here it is:
http://cariad.co.za/twhl/entitycats.php?game=3