The WELTMEISTER Button Accordion Library is an easy-to-use 
instrument, designed to get creating music instantly. Its single-layer samples contain a surprising depth and character of voicing . The VELOCITY is regulated by MODULATION (CC1), using a filter (LP1) that continuously varies the timbre as the MODULATION values change. In this way, a wealth of “hidden” accents can be added to your playing style. The Weltmeister provides seven registers for the right hand, and one for the left that includes full bass and chords.
The library needs the full version of NI Kontakt and a bit more then 200 MB of free space on the hard disc.
Update details:
1. Change the amplitude adjusting Convolution Reverb.
2. Added mechanical vibrato.
Use Sustain Pedal (CC64) to contol sound between non vibrato and mechanical vibrato.
Intensity mechanical vibrato – CC18.
Frequency mechanical vibrato – CC19.
Price: 12 USD
If you have purchased an older version of the library, lock in to your account and you can download the latest version for free.
More Informations here: Link