If you can afford it and have the time, your local conservatoire.

Piano is very different than the guitar, it is much more technique and repertoire focused (as opposed to improvisation and interpretation of guitar).

In comparison to guitar, there is much more and much higher quality material available for piano as it is being taught for hundreds of years, but most of it is accessible through classical teachers.

There is definitely opportunity for someone to create the justin guitar of piano though, I do not think it has been done yet.