Where can I get sewing elastic bands that are suitable for long-term use in chlorinated water and swimwear (elastic bands without textile/rubber)?

I unpicked a swimwear piece from "Esprit" for a sewing pattern and discovered that they used rubber, probably natural rubber, without textile (like Prym, for example), which actually lasted longer than the swimwear textile :-O

I can't find such elastic, but I would like to have it, and I need the help of the tailoring and experienced community members who are familiar with both run-of-the-mill Prym and particularly durable or non-synthetic materials.

I'm looking forward to it and thank you in advance for any good thoughts.