If you're up for messing about with some tunings outside of 12-tone equal temperament, you could try using
Tobybear MicroTuner with a .tun file (a file that basically re-tunes all your midi notes) -- a link to a big set of them
here, including several variations on the pythagorean scale, which as Bartekko said would be a good place to start -- alongside your VSTi of choice. It isn't something I've tried (although I want to - microtonality looks like a fun rabbit hole) but from the forum posts that popped up in results when I was trying to dig this stuff up just now, it's a pretty clunky setup that might take a bit of work to get running smoothly. Which from your previous posts sounds like more trouble than you're after, but it's there if you want it
![Smile :)](./images/smilies/icon_e_smile.gif)
Alternatively tune the individual notes by hand, or see if you can send different-pitched notes to different channels, and then run each channel through a pitch-altering plugin or something? -- there are lots of pitch charts for different tunings floating around Google, in cents, hertz, whatever.
Anyway this topic was about instruments not tunings, so sorry for derailing