A long while back, I had Isshin-ryu karate, some judo, and some fencing, including Barbasetti sabre, as well as various military training. I got heavily into serious yoga for decades, and have much less seriously swung rattan in SCA. The Isshin-ryu has occasionally come in handy, and the yoga has probably helped keep me supple.
I'm frankly underwhelmed by what's available in the iaido realm in the USA, as, IMHO, it seems to be a choice between MJER (which strikes me as kneeling tai-chi with a razor blade), or going to some pseudo-Toyama McDojo and expensively wallowing in Bullshido. I consider Togo Jigen-ryu and TSKSR to be the best koryu available, but TJR hasn't really propagated much beyond Kagoshima, and TSKSR, as Verity noted, is just barely here. Of the other batto koryu, most haven't spread much beyond Japan, most are relatives of MJER, and most are doubly corrupted by post-Meiji sword law and post-Occupation changes piled atop Edo-period innovations. Toyama-ryu and Nakamura-ryu (emphatically not koryu), while both are healthily present in Japan and concerned with practical application, aren't really here either, as far as I can tell.
As everybody here (so far) is a responsible adult with some practical weapons training/experience and are already cutting with katana in their backyards, perhaps the most realistic answer for us is individual study. Has anyone else here bought and absorbed Nakamura's Spirit of the Sword, and interested in discussing it?