If your device is still under warranty, call for a free replacement.
I'm not aware of any non-B&N cables that include the lit "n" and faster charging capabilities of the B&N cable--although any cable that fits will serve for data transfer and for slow (overnight) charging.
1) If under warranty, then ask for a replacement. B&N replaces cables.
2) If not under warranty then best to quickly get a replacement cable. They seem to be running out.
3) Any microUSB cable will work. Usually ones that work for things like Motorola phones etc. work. They will be slower but they will work.
Just check the Wall charger for what its power outage is. Anything that is same or less will be fine. I wouldn't recommend getting something that sends more power as Nook might not be able to handle that.
I'd recommend the charger itself be the same or higher capacity. The current draw is controlled by the receiving device and asking for more than the charger produces will overload the charger. That's why they used a custom cable -- so the device wouldn't draw more than a USB data port supplies (USB2 is five "units" of 100mA per hub, shared; so if only one device is on the chipset it can get the full 500mA). The Nook draws 500mA on the normal pins, and raws higher power via the extra pins from a charger.
The USB spec has evolved to allow for high current charge only modes which I believe work by the device not signalling on the data pins and a modern hub then switching the data into extra charge pins. Nook doesn't try that, it would be used to charge non-data devices (I have a beard trimmer that uses micro USB cable to charge).