I used sensei swivl (8 or 8.5s) and evolution curved 9 inch swivels. They are pricey! And I found some cheaper alternatives on Amazon, but they aren't as quality/doesn't stay sharp for as long. Kenchii fivestars also has a double swivel which I believe they are 7.5 inch.

ShearsDirect Japanese 440C Swivel... https://www.amazon.com/dp/B00GIJKZDE?ref=ppx_pop_mob_ap_share

ShearsDirect Japanese 440C... https://www.amazon.com/dp/B00JGIRD70?ref=ppx_pop_mob_ap_share