I was working on arcade games for couple of years. What do you
need transformer for? Are you sure it's transformer and not
someting else?
In case transformer you are looking for is the part to generate
high voltage for CRT monitor you will have to look for replacement
part that matches that unit, preferably original.
If by transformer you mean power supply, you can use PC power supply
(some games require negative voltages as well for the audio circuit but
most will need only +5V and +12V).
If all you want is AC isolation transformer, you can buy any 1:1 transformer for rated voltage in your country and power of ca 500Watt should be plenty for everything (lighting, monitor and DC power supply).
Prices (just for orientation purposes)
AC isolation transformer - ca $100
High Voltage - ca $35-100
Power supply - ca $30-100
Have fun