Here are some valuable websites for harmonica players.
Some of these sites are primarily for 10-hole diatonic
blues harp players.
A handful of websites have been deleted, or have expired.
The sites on this list are active today:
www.harpingmidi.com (MIDI for harmonica players)
http://musescore.org (create, play and print music)
www.harp-l.org (the 1st known internet harmonica forum)
www.patmissin.com (educational, reed placement charts, patents, etc.)
www.angelfire.com/music/harmonica (education & information)
www.harpinanawhinin.com (play-along charts in tablature)
www.flutetunes.com (compatible with slide chromatic; songs, etc.)
www.thetremolo.ponderworthy.com (for tremolo players)
www.tremoloharmonica.com (tremolo players)
www.overblow.com (mostly for diatonics, but has a list of useful keys and reed placements)
http://en.wikibooks.org/wiki/Harmonica/Anatomy_of_a_Harmonica (Harmonica anatomy)
www.musicstudents.com (play-along, prints music; back-up music; free sheet music)
www.dirksprojects.nl (tuner designed for single reed per note and double reed harmonicas: scroll down page to Harmonica Tuner)
www.ronimusic.com (slows down music tempos; Audio Companion for MP3; MIDI sequencer; MIDI player; MIDI converter, more.)
https://www.harmonicauk.com (present website of the Harmonica World magazine, National Harmonica League, United Kingdom)
https://getsongkey.com (song keys listed for over 6 million tunes/songs). Thanks, A.J.
Best Regards, Stay Healthy
JB