Your best bet for all things water related is Dive BVI located in the marina. http://www.divebvi.com/ They are a top great shop and should be able to help you out.
My wife, daughter and some friends over the years have been reluctant snorkels due to nose/breathing issues they could never get over. Recently got this mask, and while NOT CHEAP, it changed their whole perspective - literally . Everyone loved this mask - it will be everywhere soon. In fact we saw a rental company at Maho Bay using them.
If you are going to be in the North Sound, Dive BVI also has a location at Leverick. We have rented from them a few times with the most recent being over Thanksgiving. Their shop at Leverick are being renovated, so they have a temporary location setup on the dock.