Our old Pace Arrow rocked around a lot more than our relatively heavy Monterey, so we don't have much to complain about when winds kick up on the Oregon winter coast, or when we're just moving around inside. To us, the "instability" is almost unnoticeable, because we're used to it - it's hardly bothersome. Others may expect more and be willing to pay for it. I think this topic was broached earlier this year, and I, like Gil, discouraged the expense of hydraulic jacks. Our Pace Arrow had 4 A&E electric jacks, and when deployed they definitely made things stable. But they were problematic from time to time, and in soft or very uneven ground, required me to get out and place broad planks or plates under them. Many times I thought to myself I should just put boards under my tires, and I often did. You think it's a piece of cake because you won't have to leave your driver's seat to level up, but electric or hydraulic, you'll find yourself out there checking after each setup and prior to departures. Thank goodness for my Beaver's easier air leveling system, something the Pace Arrow didn't have.
Given the problems that many report with hydraulic leveling systems, I can't see the value in them as an aftermarket installation. The air system does just fine to get things level. Getting used to a little motion is a more valuable alternative to me. Just my 2 cents. And 26 years experience worth. If your coach is really rocking all that much, perhaps there is something wrong in the chassis.
That said, and to answer your basic question, if you have to have them I'd think any Camping World could install hydraulic jacks for you, or a diesel class A dealership.
-Joel