I suppose we have to define "qualified gunsmith". There are a million guys out there, (well at least several thousand) guys that replace parts and can maybe even mount a scope with a gunsmith shingle hanging, and a business card, that could easily make that problem worse.
I presume you mean the stock screw is loose. Several things could be the cause. Generally Marlin stocks were fit tighter than a bulls butt in fly time, but it may have been replaced, or it got loose 50 years back, and the recoil then caused the hole to enlarge and wallered out the hole, thus no amount of tightening the screw will do anything more than "fix it" for a bit.
Lots of guys plug the hole, then drill a new one, but to get that new hole properly located, is more difficult than it looks. And then the hole needs to be a near press fit, or a two step hole on the screw diameter to really be correct, and not loosen up first trip to the range.
Shipping guns at present, can be a headache and expensive at that. I am sure several guys here know someone that could do the work, given it could be shipped in a simple manner. As far as I know, a gun can still be shipped to a gunsmith, and returned to same owner, but dont quote me on that. But then Fed Ex or UPS has its own hoops to jump through.
In any case, the job isnt rocket science, but you need to find a guy that has worked on such jobs before. Do not take it to your local 1911 expert, and expect him to really savvy the correct repair. He might or might not know. It would depend on his background in guns.