a) somebody powerful finds out about the party having these weapons (after all, it's goign to attract attention once they start trying to find a buyer -- this is not small change dealings, but instead trying to sell -major- weapons on the free market).
b) this person sends word to the party that he/she wants to see the validity of the items but will pay handosmely for it
c) the party has adventures just going to this far remote place (perhaps the person is on their own island, etc, or else just off on the far corner of the continent).
-- some (but not all) of these adventures include keeping robbers from trying to steal the weapons
d) they finally get to the person and have to RP (or skill challenge if doing 4e and you like skill challenges) the explaination and display of the weapons -- and which PC wants to be the guy demonstrating the deck of many things?

or show how the mace of st culthbert hurts...
e) the buyer could ...
1) try and take the items by force after the demonstration
2) try and convince the party to give (or greatly discount) the items (or one specific item) giving the reason of representing the rightful owner (such as a church of st cuthbert, etc)
3) buy the items (legitmately and for a large sum of money) from the party. but then a couple months later, this buyer has equipped his soliders with these same items and they are starting a war. thus, all the money the PCs got from it will feel 'dirty' since they just supplied a war that is killing thousands and the buyr and his forces seem unstoppable thanks to all the power that the PCs sold to him
basically, just think of different movies/books/shows/stories about weapon deal exchanges, and all the ways those things played out..