Patto, I have no first hand knowledge of this subject & don't know of a local supplier. I do remember reading an article on this subject in the ideas locker section of the April 2016 edition of cruising helmsman magazine. The author had the same problem when he wanted to reseal the pontoons and then repaint them along with the rigid hull of his 3.1M inflatable . He used product made by Inland Marine who have a stockist in New Zealand. The products are water based and can therefore be transported by air. He quoted a postage cost of $35 for the goods which included inflatable sealant($79.95) for the leaks, topside paint x 2 ($99.95), Polymarine adhesive tape ($50), primer & enamel ($95). He stated you could save $135 if you painted the hull the same colour as the top sides rather than using different colours as he did. Please let me know how you get on as I intend do this myself some time in the future.
Thanks Fred.