Glenn mentioned sand. Go for "sharp sand" or "washed sand" as we call it here. It's used for concreting. "Fatty sand" is used for bricklaying and has a certain amount of clay and stuff mixed in with it hence it's orange colour. I have never bothered with it as my mentors always use sharp sand. Suck it and see and let us know how it goes. Please don't report back saying it's a bit gritty in the mouth
As for borax if you can't find it in the shops ask Grandma, she might have a box of it somewhere :wink: