Order them through Gael Force Marine (Inverness) or Cameron at Clyde Outboard Services. Both Tohatsu dealers/agents. They will no doubt have to order from Tohatsu UK, will come with standard £5 shipping charge on top.
On a Tohatsu 2-stroke 60/70hp/90hp+ the part number is 3B7-83715-0.
Also needs a washer (353-83719-0) and locking 'R' pin (951603-0800)
This is a useful site for part numbers. Tohatsu Outboard Parts