Remember seeing these a couple of years ago, then forgot all about them until I read your thread.
Checked out some reviews, and seem to do a job.
http://www.amazon.co.uk/Valiant-fir300-Stove-Fan/product-reviews/B00748I2MO/ref=sr_1_1_cm_cr_acr_txt?ie=UTF8&showViewpoints=1
http://www.amazon.co.uk/First4Spares-Powered-Burning-Silent-Friendly/dp/B006ZX4NJA/ref=sr_1_2?ie=UTF8&qid=1347501148&sr=8-2
http://www.amazon.co.uk/Ecofan-800-Black-and-Brass/dp/B0012MD796/ref=sr_1_3?ie=UTF8&qid=1347501148&sr=8-3
http://www.amazon.co.uk/FIRST4SPARES-UNIVERSAL-Powered-Burning-Stove/dp/B006ZX27LQ/ref=sr_1_4?ie=UTF8&qid=1347501148&sr=8-4