Here is a list of parts, searching ebay (worldwide) directly for the quoted items should allow you to buy the same ones that I bought from China.
15w Amplifier - "ta2024 amplifier "
Bluetooth module - bluetooth audio receiver usb"
Voltage converter - "12v to 5v buck step down"
Battery charger - "SC Fast Charger for NiCd/NiMH batteries Vapextech"
Ground loop isolator - "ground loop isolator"