Waltz Received Potency +3% exists on a drop (ring) that was added to the test server a while back. It is pretty much only useful for self-Waltzes. I have all the gear that Zhronne listed, and I was (functionally) never limited by the Waltz cap because I never use Phurba.

This does not really solve the feasibility issues with Waltzes or make alternative methods of increasing potency any more viable. As I have suggested in the past, SE should lower the base HP healed a little and increase the multiplier for the (VIT+CHR) term for Waltzes. This would let us pump up our Waltzes a little and would rely on a stat other than Waltz potency to do so. Adding 40 CHR to your Curing Waltz III set (with +25% potency) only increases your HP healed by 37 points. Isn't that a little ridiculous?