I doubt you will get a motor for your drill.
The drills will very probably have been made in China with component parts (motor for instance) also made in China and sourced locally.
There will have been no economic benefit shipping a few spare motors to the UK - if a motor failed they would want you to buy a new drill rather than a new motor.
The flippant answer to your question is China.
You might try Solent Tools but be prepared for disappointment.
http://www.solenttools.co.uk/p0/performance-power/314604.htm
Peccavi
June 2013