When I looked for something similar a few months ago, the answer was no. There are 30pin adapters out there, for use on Apple plugs, but they do not work for the Nook 30 pins plug. The Nook 30pin is proprietary.
But someone else may pop in with a different reply.
Did you know Nook UK has all the Nook accessories, including chargers for £5 each at the moment?
Thats a huge saving on what are usually expensive cables and accessories.
I am not sure where you live, but I live in New Zealand so I had to use a freight forwarding company to get some spare cables and new covers shipped to me but even with the extra shipping costs, it still worked out a good deal for me.
I understand you are wanting to make use of what you already have, not buy even more cables, but you may not have that option, so at least some spare cables would be handy.
http://www.nook.com/gb/store/accessories