Google 2 part pour foam & you should have no problems finding it. I know Jamestown Distributors carries it. You can also go with closed cell block foam. It's a bit more tedious to install, but won't absorb water over time.
I think once you remove the pourable foam thats in there you will not want to ever see or use it again. From researching the restorstions on here I think the blue or pink foam is the way to go. Not being familiar with fiberglass boats I would be curious how much structure the foam provides. You may have to use a pourable foam.
