Make one out of cardboard - you can buy large sheets of thick black card stock or "poster board" from any decent art supplies shop. Or just spray paint it when you've finished.
For Sony Trinitron screens it should be a little easier as they bend in only one plane.
Check out this thread, over 20 years old, on making a "
$2 cardboard bezel".
You could also check out my own efforts for my
Aussie lowboy cab.
Bobby13 even made a bezel out of fiberglass. Search the forum if you are keen on that.