Hi Ian
Welcome
Start by making a list by looking at the capacitors installed in the preamp. Keep an eye out for bipolar capacitors, if any. For 1uf and smaller values, you can use film caps. You can increase the voltage of capacitors but not its value. Eg. If there are 3 caps with value 10uf and voltages 6.3 volt, 10 volt and 25 volt, you can buy 3 caps of 10uf 25 volt instead of 3 different voltages. Dont go too high in voltages as they will get physically bigger and may not fit in the space.
Preferred capacitors are elna rfs, nichicon fg or kz, panasonic fc or fm. You can buy from mouser or digikey.
While installing ensure the positive and negative terminals are correctly oriented.
Regards