or try Watch Obsession in the UK. I think there are a few others also in the US that specialize with Isofrane rubber straps. I believe a reputable reseller on WUS also has a few in stock. I usually get them through the official channels as they are made in Italy π€·ββοΈ
BTW, get the RS buckle which is the squared off model. I just posted 2 Isofrane rubber straps for you to see.
The RS buckle is square and the IN buckle is rounded