...some places to try -
If you're in the UK (or if not - they might ship abroad, it's worth asking) try Retro Exchange in London - telephone 0171 692 1213
Alternatively (again in the UK) try one of the several Computer exchange shops around London. The one at Notting Hill has loads of old stuff. Sorry I haven't got their tel number. If you buy anything I would suggest asking to see it working before parting with your hard-earned.
Also worth trying is the ever popular Ebay-
Ebay - UK Ebay - US
If you have no luck, why not go for the excellent
Intellivision emulator
Jay