I doubt you can order this in the US, since it's not in US cars.
The wiring may be there, but the heating elements won't be in your seats. You'd have to replace the seat and/or seat cover.
I'd contact Mitsu directly and ask them for this feature. Then one day in the future you may have the opportunity to retrofit it. Let us know what they say.
Or: start a new thread with a poll and get US owners here on the forum to voice their requests. I'll pass it on to the PR rep for the company if people want it.