funny you mention this, it seems that many movies are shown open matte on tv channels I know for sure show some open matte movies are
AMC
FX
FXM
BBC America
SYFY
I noticed if it says “this film has been modified from its original version, it has been formatted to fit this screen” theirs a good chance of it being open matte
I know someone asked about x-men fx showed the last stand and its on demand on fx too and it displays this message