Etymology and distribution of 許柯.

Kyoka 【許柯】^{レベル1
Very rare}  The Japanese surnames etymology dictionary.

Fukushima-ken Tamura-shi , Saitama-ken , Toukyou-to . 石沢 surname available. Fukushima-ken Tamura-shi Fishing boat town Hokka - cho is based. The place is the origin. 石沢 Ishizawa reference.