I cannot recommend any person in particular; however, most of these older air rifles are pretty easy to repair with just a few tools.
I have a Wagria Model 50 and recently replaced the mainspring and breach seal. For the main spring I used a Diana model 5 pistol spring with three coils removed. The old breach seal was replaced with an oring. All of the Wagria models used leather piston seals and they usually are usable if they have not dry rotted. The old lubricants are probably dried out so a simple clean/lube would also be in order.
You can email me at hudsonhw77 --at-- gmail.com if you want to.
Paul in Liberty County