Trouble is with English guns is that there are all 'one-offs'. Even pairs don't have parts that interchange. There are odd exceptions by Bonehill, B.S.A. and Webley & Scott so your only hope is to have the part made by a Gunsmith.

I would like to know a bit more about your Fry gun if possible. Since posting the above I have acquired a further Fry hammer gun in 16 bore. Lagopus.....