Check with Progressive Epoxy at www.epoxyproducts.com. They are good,
responsive people with an old fashioned (e.g. no glitz) informative
website. They market a wet/dry product that can be used underwater:

WET / DRY 700: UNDERWATER EPOXY PASTE
The very lastest generation of underwater epoxies, Wet Dry 700 is
Kevlar (tm) filled, underwater (or dry surface) epoxy paste. Thick but
workable at low temperatures. Use as a thick coating or repair paste,
with or without fiberglass cloth. Easy 1:1 mix ratio. Color: white.
Non-hazmat and available for export outside the USA. Can private
labeled for resale. A lot of our 1 quart kit sales are used for
fiberglass swimming pool repairs underwater. This product is about
wall mud thick. To make thicker (i.e. like bread dough) add some of
our EZ thick thickener....

Steve Hayes