Classical music concert sites or an ap to help us discover live performances throughout Europe

This is a rather bizarre request , are you looking for recordings for a phone or tablet ? or live performances ? Not meaning to be snide , but you'll never find Tchaikovsky spelled that way ( even in Russia ) . Recordings are ubiquitous on YouTube . My wife and I often listen on a tablet while having a relaxing dinner in our hotel room . If you are looking for live performances , it would help to know where you will be and when /

Operabase will give you an answer for opera productions.
http://www.operabase.com/
For Madama Butterfly from September 1 to Oct 31, I see Gothenburg, Stockholm, Warsaw, Venice, Hannover, Muenster.

For classical performances.
https://bachtrack.com/find-concerts/category=1;freetext=Tchaikovsky%20Piano%20Concerto;medium=1,3;work=7001

As you have changed your original post , it is easier to grasp your plan now , Sam's suggestions are ( as always ) great , but I think you are approaching this in a somewhat illogical fashion . Allow me to explain - Looking at the site for classical performances , I see one with The Tchaikovsky that would fit your wishes - Sunday , 14.10.2018 . 11:00 at The Concertgebouw in Amsterdam , Anna Fedorova , soloist . If you are in Amsterdam , a great choice , but what if you are in Vienna , or London at that time ? It will make more sense to look at the various venues available relative to your anticipated dates of stay , rather than planning your stays based on a certain performance . If you are in Berlin , see what is on with The Berlin Philharmonic , In Vienna , look at The Musikverein , In Paris see what might be at The Palais Garnier , etc . In any event , this performance of Anna Fedorova at The Concertgebouw of The Rachmaninoff Concerto #2 in c minor is truly spectacular , one of the best I have ever heard , enjoy ! https://youtu.be/rEGOihjqO9w

Another challenge is that even if you find what you want, the performance in the middle of an ideal itinerary you may have constructed may be sold out by the time you try to buy the tickets. Note that event tickets are never returnable. I will say that I have had good success with those internet tickets I have bought in advance, even when the house policy is to mail me the physical tickets. Remember that your credit card company may freeze an international transaction.

I cannot help with specific performances but Classictic.com will allow you to explore what is on by city and date.

Laurel , that's a great informational site . It will be interesting to see how far into the Autumn season they list , once tickets start to become available . From the perspective of purchase , I would be inclined to buy direct from the venue web site . A very useful addition to my " toolbox " .

So what's wrong with using live performance dates as the jumping off point for a trip? People use hobbies or events to kick off trips often. I think,it is a g reat idea to review dates and places, then build travel around that. There isn't a 'wrong' way.....just a different way.
Zagfam, hope you can find what you seek and build a great trip.

Maria, last summer, we saw Alvin Ailey American Dance Theater in Frankfurt, went to Berlin and Baltic Germany for some specific places, and then saw AAADT in Copenhagen. I didn't belittle the OP. I listed some drawbacks and practical matters. That's what a newsboard is for.

I'm willing to sit in any seat and don't care about the price. And I'll change nights to get into the theater, with a different program. But last time we were in Vienna, we settled for the opera that was available to us.

It was the specific, non-negotiable, warhorse repertoire demands in the OP that were ... ... odd. I go to 50 to 70 nights of concerts and theater a year. I love it when other people support live performances.

The OP's remarks struck me exactly as Tim describes . Furthermore , the poster rewrote the original post , which was rather convoluted to begin with ( no offense zagfam ) . As well , no one was attempting to dissuade the OP from seeking out these performances , only how to accomplish this without aimlessly bouncing around the continent without a cohesive approach .