The gadgets that close the reeds off so that they dont sound when they are not supposed to can be fabricated out of polythene and stuck on with wax or sooper glue.
There are several 'Larry Adler' publications about playing and as usual these assume that you can read music in at least a rudimentary way.
My local music store had a video tutorial but yesterday when I went in ( to buy a really nice guitar ) it was not there.
I have a hohner chromatic gob iron and it has square holes which can make your mouth sore. There is another use for vaseline here.. Hmmm.
Hope this helps. It is a terrifically versatile instrument in the hands of someone like Larry, however there are some really very good Irish players who play traditional Irish jigs and reels on them.
Can't help much more than that.
Hohner do repair them but that can be expensive. Mine cost about £45.00 and that was ten years ago so they must cost a lot now.
Best of luck, persistance is everything.!!