Looking for guidance: unchoked, fast twist barrel for Hatsan

The factory Hatsan barrel seems to have 1:17.7 twist rate. I am trying to get 1:14, unchoked barrel for a benchrest experiment.

I have never tinkered with barrels before, so I am wondering where I can buy such a replacement barrel from. Do I need to take it to a gunsmith to get it fitted, or is it just a thread-on?

Any pointers are appreciated!