From 1960's on, thyristors ( scr) were usually for high power conversion, not for consumer markets.
With gate drives of ~ 1 Amp peak, fast risetime and long duration, and control feedbacks of 400V ~ to kV levels ,
and a multitude of topologies, there was probably little ability or commercial incentive for development of generic ICs.
( That is in comparison to say, SG3525 etc that could directly drive FET or IGBT in pwm for lower powers and voltages)
In my experience, particularly in UK and EU, the manufacturers would encapsulate their own control circuits and give an OEM part number.
If the equipment you saw is old, perhaps that is the part number.