to the forum.
What's your budget?
A replacement transformer may be difficult to find.
Those amps, in their entirety, can be had used fairly cheap.
A doner amp may be your best option.
Because of 230VAC assuming if you are European, when you find out the specs and dimensions check Piemme-Electra in Italy. They call PT "input transformer".
Hammond provide detailed specsis and is widely available, possibly locally?
EI-core transformer has three different mounting options and when electrical/mechanical specs suit it is easy to change different. Piemme sell mounting legs/end bells for DIY but should also change it reasonable cost?
Possibly replacement is not available? Nowadays installing two or four Toroidal transformers is valid option because they are cheap and small.