Can the lock be replaced?
Sure, but will involve condsiderable work on your part. Today's Davis and L&R locks are far superior to that on your rifle, plus spares are readily available.
Assuming you've not done a lock swap before:
The Track of the Wolf catalog has full size images of various percussion locks: find one that has about the same length lock plate. If the replacement lock is "slightly" larger, you may be able to modify it to fit the lock recess. You will need to make/modify the area where the drum fits. Select a version that does not have the recess already cut, so you can adjust the placement to fit your barrel.
Now see how the hammer nose strikes the nipple. Some cold bending can achieve a good fit. Buy a spare hammer as you will probably crack the first one when trial fitting ... but now you know how far to bend it.
See where the lock's sear and trigger bar mesh. If you are lucky, it may work OK with the A&H set triggers. Otherwise, anneal the sear and bend it slightly. Buy two as you will likely break the first one,
Or buy a new tumbler of about the same size, complete with stirrup, then fit it to your lock geometry. Machining & re-heat treating will be required.
Or buy a stirrup of about the right size and fit it. Much filing and trial fitting will be required. And know that you still have a basically Spanish lock of unknown metalurgy.
The replacement/repair won't be easy but give it a try, as the alternative is a wall-hanger. Don't give up.
