First place I checked, saw that they were out of stock.
In the photo, the peg at the top is a spring loaded plunger; fixed peg on the other side. The pin pivots the lock to the bolt. The rectangular slot surrounds a lug on the firing pin. No doubt prevents the firing pin from moving when unlocked.
Meroh - thanks for the offer. I may have a go at making a piece, will let you know.