The wrist strap used in MAXREFDES101 is a generic 22 mm quick release wrist strap but it can be any 22 mm quick release.
We used this on our HSP2.0:
https://www.amazon.com/gp/product/B01LY4Y17H/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
However, we would also recommend the below options. The wrist strap must be very flexible to ensure good contacts between the optics and skin is obtained at all times. Therefore, the below flexible nylon materials are recommended.
https://www.amazon.com/Compatible-Runostrich-Lightweight-Breathable-Replacement/dp/B07P17JNQG/ref=sr_1_4?keywords=22mm%2Bquick%2Brelease&qid=1555698682&s=gateway&sr=8-4&th=1