This doesn't make a whole lot of sense to me. Right now you should be harvesting pumpkins not pumpkin honey. Any honey produced from a pumpkin patch should have been taken off months ago after the pumpkin plants had blossomed. Before the bees moved on to another source. This is about the only sure way to get the floral source you are after. It would also mean that the colonies were taken to a rather large pumpkin farm for pollination. If colonies were doing some kind of pollination and then taken to another location or even stayed in the farm after the bloom they will move on to another source. Any frames that weren't filled with pumpkin blossom will be filled with wildflower. Of course there is a possibility that it was all sorted, I guess.
My mentor, from smell, can tell when the bees are bringing in honey from goldenrod and I would assume that the same could be done for pumpkin. But to my knowledge the above is the proper way to collect a specific floral source honey.