DVD's from Dirk Powell and/or Big Nick to start with.
Also youtube on youtube/facebook you can find information
There are also pro's who give lessson online
If possible a teacher right in front of you isn't bad either.

The only one row with spoon bass are Hohner H114
Most one row players play their accordion with a thumb strap

For your other question about builders.
There are a lot for years, but not many with a website.

If you search in Google for "cajun accordion builders"

Marc Savoy, Larry Miller(with his grandson) and Junior Martin were called the big three and they still are active.
The late Mr Randy Falcon made beautifull accordions and Rusty Sanner now made accordions like Mr Randy Falcon did, with the brand name Heritage.

Other names:
Andre Michot
Graig Vincent
Jesse Lege
Jude Moreau
Ed Poullard
Tim Reed

I don't know if they are still building
I'm sure that I forget a lot, but this ones I know