The 44TB2 SCR appears to be a 200V 70A device. I do not see what package it is in. If it is running at a high current, then it will need to be fitted properly into a heat sink.
It depends on which country you are in for the best place to look for a replacement, in the UK.
RS
CPC
Farnell
Cricklewood Electronics
are some places. You will need to sift through the devices available.