Threaded studs is a big reason why I don't like Stihl; it's an unnecessary potential headache, and they don't even loctite them from the factory.
I just clean the threads on the stud and the hole very well. To do this, I leave the saw starter side down for a while after draining the oil to get the residue away from the stud side. Then I get several Q-tips (the made them slightly smaller now, so they may not work as well) double over the tip of one or just pair up two and thread them in the hole, and out again. I do this a few times with rubbing alcohol, then dry to get the threads squeaky clean. The studs I wrap in a paper towel and dig my thumb nail into the thread groove and twist, repeat until the groove is squeaky clean. Then I thread the studs in tight with blue thread locker. You can thread the studs tight with either vise grips on the part the bar sits on, or tighten 2 bar nuts against each other and use a wrench, or wrap the threads with leather or something like that and use vise grips.
I wouldn't chase the outer threads. Maybe just a drop of oil on them since they don't need to be super tight. A tiny screw driver can scrape out the gunk if there is any.
I really doubt dealers wouldn't carry old style nuts since they are so common and are better than after market ones, but maybe the AM ones are outselling OEM too much.