Hi Lex!
Look, i searched some information on the orientation page for Nagasaki
https://planetyze.com/en/japan/nagasaki/orientation
and with what i learned I searched google and found these guys who do exactly what you are looking for:
https://www.facebook.com/wavepeak.sasebo/
Wavepeak (or Wave Peak) Kayak in Sasebo City & Saikai City 99 islands in Nagasaki
Why don't you send them a message on facebook?
I Hope it helps!