I hate to be the one to bring bad news, but parts for those little Belgian guns are next to impossible to find, since they have not been made in about a century. Both parts would probably have to be made and finding a gunsmith who can and will do the work is also going to be about impossible. The really bad part is that the guns are worth very little (less than $50), either as shooters or collectibles. I am afraid that repair would cost many times what the gun is worth, even if you could get someone to do the work.
The reason I say that about gunsmiths is that work of that nature is a thankless job. A gunsmith may put in several days working on the gun, then when he presents a bill for maybe $300, the customer decides the gun is not worth that and refuses to pay. Been there, had that done to me. Too many times.
Jim