I got it off AliExpress - seller: V4 Watchband Store. Cost me €21.- Today I found one with another seller (SmartWatch Strap&Cases&Tools Store), also offering two different clasps but otherwise seemingly identical product. €14.- Search for "sharkmesh bracelet 20mm" and pick the one you like most.
20 mm width will fit your Sumo
Be sure to order the correct length because length adjustment is done with the fine adjustment in the clasp only.
You will need custom spring bars, 2.5 mm thick bars will not fit - and normal spring bars with a .8 mm tip will sit too loose in the watch. I use 1.8 mm thick spring bars with 1.1 mm wide tips in mine. You'll find those on ebay or AliExpress in case you don't have them already.
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