Where can I find tank safe expanding foam?

I see in a lot of aquarium videos from American YouTubers, they use an expanding adhesive foam to stick rocks together and fill in the gaps between hardscape. I have attached a picture of the one they commonly use, but there's multiple products available in America.

Does anyone know where I can find a water safe expanding foam in South Africa? Or perhaps just suggest alternatives for a product that I can use to fill gaps between hardscape and adhere rocks

 

Any one-component polyurethane-based expanding foam (suck as Sika Boom) should be okay if it doesn't contain a biocide of some sort. Avoid the two-component expanding foams containing isocyanate.