Great, thank you for the help. I emailed them to see what type of information they had.
I'm fairly certain that it was built on a Voere action -- unfortunately, the current Voere company (now in Austria, rather than Germany) said they do not have a trigger that would fit. There's another custom maker who used to use Voere actions, in Seguin, TX. I'm going to see if he has any suggestions on what can be done to the trigger.