on my 98 road king, i went with 16's and poly bushings. i could still feel them move around on me some. when i changed to 18's, i had a buddy make me some solid steel riser bushings. i loved them. the combination of those and a one piece clamp is the deal.
to answer youre question, i havent seen anyone selling them anywhere yet though. and no, the vibration was no issue at all.
one thing to consider on apes and movement though. i occasionally go up under my nacelle with a 3/4(?) wrench and tighten the lower riser bolts. you can get to them by turning the bars all the way each way. you'll be surprised how they can loosen over time. a simple torque or two makes a world of difference in play. check it out.
head