Try Nook accessories section
Nook
http://uk.nook.com/accessories/unive.../9780594515364
I lost my charger for a week and spend ages trying to find a spare cable on ebay or Amazon - but all I kept finding was chargers for the reader.
I went in to John Lewis - where I bought my Nook HD - but they don't carry spare chargers to buy ( apparently similar situation for the Samsung tablet).
Blackwells sell them (on line) but you have to pay postage (didn't look at what the Nooksite said).
I eventually found mine - where I'd left it of course - and when charged my Nook welcomed me back, Grrrr!
Hope that helps