This could be why you were told that there are no available records. Until 1836 the only legally recognised place to get married in England was an Anglican Church. In Northumberland, non conformist folk would often nip over the border and be married in Scotland, or just comply and get married in the Anglican Church.
If you'd like others to have a look and see if we can find anything that may help, post the details and someone may be able to come up with something.
Boo