Hello~I can relate to your frustration, I have them too, although not as many. I often wonder how it can be normal, but they say it is when the heart is "Structurally healthy" I have found a lot of help from Dr Sanjay Gupta, he is a cardiologist from York, UK, he has many videos about palpitations and a Facebook page, they area big help to so many that have issues such as yours and mine. Here is the link to one of his Youtube videos, from there, you will be able to find many more.
Well the word I got in a similar situiation was that Pvcs are not life threatening. Or perhapes not "as" life threatining as other heart beat issues. My Doctor informed me that every (Even him) have pvcs maybe x amount a year and then he read the Holter and said "And you have 5000+ a day???" We discussed the dangers associated with trying to burn out the signal source of the wacky heart beats and I told him that I felt like I was going to die everynight from all the drunk bongo music my heart was doing. The procedure was painless and was all done with a catheter and some injections to make my relax because I had them mostly in bed. The doctor also tried revving up my heart rate but the Pvcs weren't as bad that way. Have a good think on how your quality of life is going and if 1000s of missbeats are freaking you out push for a solution.
It seems like the cause/trigger is different for different folks. I tried all that stuff you mentioned as well and nothing happened. Then I tried taking supplements of Taurine and L-Arginine and the PVCs stopped after a week or 2. That was after a year+ of 10-20k per day. I'm continuing to take my low Metoprolol dose and the supplements because I sure as hell don't want these things to come back!
I say all that mainly to say that there are probably a few more things worth trying. :-)