Patrick has called this one, Yes horrible is a good word. But a simple fix and maybe even with that striker.

You will have a tough time finding another .303 striker, but one can be made from a .577/450 also. IMA sells replacement for the 577/450. British Martini-Henry Type III Striker: Unmarked - International Military Antiques

It should be a simple job for your gunsmith to turn one down to fit.