For the 2N4304 you can use MPF102. The unmarked capacitors below 1uF, use 100V or more, mylar, polyester or ceramic (last resort). Since you have an amp, look at the parts in the amp for a voltage rating.
Transformers will be difficult to find. Mercury Magnetics makes a replacement for the driver transformer, but it's very expensive. For the power transformer I know of no available replacement. The easiest thing to do would be to find a used Concert amp (Lead, Bass or Slave) and use the power transformer from that. If you need a 220V or 240V primary, you'll have to have a transformer custom wound. The used amp will also have a driver transformer.