There are quite a few small artisanal mozzarella makers. I live in New York City and there are 3 in walking distance from my house! They make quality cheese and may also have more control over the specific cheese characteristics if you ask them for it. I don't know if it makes sense for you to get cheese from the US, but if it does, use Murray's Cheese (
http://www.murrayscheese.com/) or Artisanal (
http://www.artisanalcheese.com/). If this is for a business, give Jason at Murray's a call and he will hook you up with the best Mozzarella you can ever dream of. They even have fresh Mozzarella flown from Italy! Formaggio Kitchen is also another good source - they specialize in genuine Italian artisanal cheese import and sale (
http://formaggioessex.com/artisan).
I suspect as for your grand question of "what happened to the Mozzarella I knew and loved" the answer is in economics. There are two common ways to create Mozzarella. The first is the classic one, acidifying fresh milk patiently with natural cultures until it's right and then coagulating it, cutting the curd, heating the curd pieces up and when they begin to melt, kneading them skillfully and braiding them, or turning them into a ball or tiny bocconcini.
The other method is quick acidification. Usually done by using citric acid or acetic acid (plain vinegar). That affects the flavor of the cheese as well as the meltability and "bite" of it because the melting character of cheese is direct result of how much acid is in the cheese. This makes an expensive 2 hour process into a cheap 5 minute process and it is obviously the favorite of many industrialists. Having the cheese stretched and kneaded by industrial machine contributes to poor texture control. Also, the larger the factory, the worst milk quality goes into it. You have a mix of milk from cows of different regions that are fed junk food and injected with hormones and over-milked - you will get flavorless milk that seriously lacks in enzymes and minerals which are the basics of texture, flavor, stability and process in cheese making. Such milk is so poor that it typically must go through violent pasteurization -also to enable it to go through long term storage and cross country trucking (forget fresh!). Such is the story of industrial food.
I say, go to cheese stores, get genuine artisanal cheese from small quality farmstead producers. Sure, the price will be higher, but you can tell why when you eat it. It will take you back 100 years to the real honest food you have been looking for. Worth the premium in my opinion.