The SIS and Accushift stuff start at 6 speed. The advantage there is that a lot of bikes won't need to be spread going from 5 to 6 speed.

There's lots of ways of getting the shifting on TO the bars. For me- it's been a problem of what's comfortable on the bars, and what seems adorably acceptable in my "vintage" sort of idiom.

The immediate solution is bar end shifters- lots of people love 'em, lots of options. Score a set of the Suntour Barcons for $30 and you don't have to change a thing on your bike. There are solutions like the Retroshift and Kelly Take-Offs that mount other shifters near the brake levers. My personal favorite has been the Suntour Command Shifters. They mount inboard of the brake levers, so they're right there where my hands are where I ride 90% of the time.

You could also get creative since you've probably got "turkey levers" and take off the inboard brake lever extensions and fabricate a mount right onto the existing hole/stud for that...

If you post your ideas of where you're headed- I'm sure there's plenty of people here that'll love to help you get pointed in the right direction.