Hi Antonio!
I got the mini holder from Aliexpress for about 40 bucks incl. shipping, it is called "precision bench vise".
The hand stabilizer is a very simple but genial tool - you hold the stick between your middle finger and ring finger and the tool provides slight counterweight and friction - thus your hand is much more stable. I was a bit suspicious first, but I have to say it works like a wonder.
Cheers
Ondra