The Castagnari "Melodeon" is a 1 row 10 button, 2 bass, diatonic, bisonoric bellows driven aerophone. with four stops with LMMH reeds. It is built to a very high standard. Theor standard reeds are Antonelli tipo a mano. I believe the current price is $2750 US, you can check that at the Button Box. They have a web site.

Castagnari generally tunes 12TET from dry through a variety of wet tunings.

I have never heard of one tuned to "just" tuning..

I would not buy a Castagnari tuned to "just" tuning nor would I have one retuned to "Cajun" tuning.

Thought this could be done, I would not advise it.
The Castagnari is not a "Cajun" box.. it is something a bit different. You would need to see and play one to understand that.

When I had one in C stupidly sold it) I played Cajun tunes and they sounded fine.. though not dischordant. (to my ear)

The link shows Brendan Begley playing an older model with an added extension on the fingerboard because he has such long fingers. New ones look the same as this one minus the keyboard addition.

Just make sure you don't open the air valve : )