Start here:

http://www.martinihenry.com/links.htm

• T.W. Chambers and Co. http://www.chambersgunmakers.co.uk/ Spare parts for BSA Martini 12/15 and international
• John Knibbs International http://www.airgunspares.com/ Search BSA by model
• Jim Hallam http://www.classicguncompany.co.uk/
• Gun Parts Co. or Numrich http://www.gunpartscorp.com/
You need a firing pin/striker for a small BSA martini or a Cadet Martini. Send these folks an email and see what the have. Contact them in the order listed. Gunparts would be last choice.

Can't tell what model it is but it looks to be in the Model 12, 13, 15 or 1215 family.