FWIW, Trigger job on your 43 Spanish RB, which I assume is an 1879 model Argentine, is actually quite simple. Something you should be able to do yourself.
Find instructions for disassembly of your rolling block action.
Once action is apart, you will find two flat springs held by screws, one much larger than the other. Under the larger flat spring is the smaller one. You will need to remove larger flat spring to remove smaller one.
RB trigger job is just thinning out the smaller flat spring. This spring accounts for the heavy trigger pull. When I did trigger job on my 79 Argentine RB I beveled out the sides of this spring, thinning it about 33 %. Used a bench belt sander to do my spring. Some just thin along one flat side of spring along the mid part of the flat spring. In other words, leave ends of spring alone, just thin out middle part. This is what your gunsmith will probably do. When I did mine, certainly made a big difference in trigger pull. Just depends how much metal you remove from spring, how much you'll reduce trigger pull. Of course, remove too much, you have a problem.
Google Rolling Block trigger job, you'll find info and probably a replacement wire spring sold by someone in California. You may be surprised by how small this wire replacement spring looks.