I live in the UK and picked up 2 Nova heatercores on Ebay for 8 quid each, including shipping.
They are exactly the same as the chevetter heatercores everyone on here uses. I've attached them both to the sides of a server case so it'd run passive.
They're very fine bits of kit.
Do a search for "heater" on ebay.co.uk as some people list them as heater-cores, some as heatermatrixs, as well as some other things.