I don't know if this is the same one but I got it for my 6X.
https://smile.amazon.com/gp/product/B081PXR4JP/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&psc=1

Nice find! I need a leather band for my 6X and found the same band on Amazon but in the 26mm size for the 6X. Link

TRUMiRR Watchband for Fenix 6X/6X Pro/6X Sapphire/5X/5X Plus, 26mm Quick Release Easy Fit Watch Band Genuine Cowhide Leather Strap Sports Wristband for Garmin Fenix 3/3 HR/Descent Mk1 https://www.amazon.com/dp/B081PXR4JP/ref=cm_sw_r_sms_apa_i_nVzWEbY43K7E6