One of the best opportunities for training with great paddlers has now become common at major paddle races. The biggest surfski and outrigger races typically draw many of the world's best paddlers some of whom provide either multiday training or daily training runs that you can sign up for well in advance. Downwinders in surfski or OC doubles with a champion can be an eye opener. Races such as the Gorge Downwind Championships,
Canadian Ocean Racing Champs (on hold), Maui to Molokai, and The Doctor will have several training opportunities that will be advertised (and often fill up) well ahead of their associated races.
There are now some companies that are combining training with full support packages for your paddling centered around some well known races. Packages can include accommodations, coaching, paddle equipment, all race related logistics, etc.
The list below is supposed to primarily include sites/places that are more or less permanent locales for multi-day training. Notice that a number of the online coaches will schedule intermittent training camps based on demand in various locations. So it can be worthwhile to check with them about scheduled trainings with open signups, particularly if you are looking for one that might be closer/more convenient for you.
Spring Camp 2018 Haverdalsbukten/Halmstad