As a tyre dealer, I buy from all the suppliers of repair materials. Sealtite, Rema, Beissbarth, et al..
I also retail repair kits. After years of reselling kits from the above suppliers, I choose to stock Ironman kits as they offer really good value for money.....
I suspect that the source of the repair materials in their kits, and the source of the repair materials in the bigger competitors is not too dissimilar.