WHICH transformer? Output or Power?
The output transformer is 70500203 Peavey part number. I imagine now 35 years later, that Peavey no longer has them in stock. Any 50 watt OT suited to a pair of 6L6 would work, the Classic 50 uses EL84 though. The problem is that this amp uses the ultralinear taps. A transformer with UL taps is less common. You have the alternative of adding screen resistors and wiring it up conventionally.
The power transformer is another story. It needs the standard HV winding to provide 500+ volts for B+. And enough 6vAC for the power tubes. But it also needs a 40vCT winding to make the 15v rails for the preamp.