Gentner TI/GT Wired 6 Button 4 LED Conference Hybrid Remote Control 910-110-100 [New]
( 232646459767) )
Gentner Phone Hybrid TI/GT Remote Control 910-110-100
New Old Stock, Open Box
Multiple item listing, so there will be some small variations between units.
These tend to be the part of systems that get the most abuse and replacements are hard to find.
As you can see from the pin-out information, it's essentially a simple device with buttons and LEDs so I see no reason why it couldn't be adapted to be a useful button box for other broadcast or AV equipment with GPI connections.