First, you waited too long to get the tires rotated. Tire manufacturers recommend rotations every 5,000 to 8,000 miles. If you don't do that you run the risk of irregular wear - which you've got.
Second, the real culprit here is alignment. Regular rotation keeps the irregular wear due to alignment in check as the tires develop a different wear pattern in different positions.
When you go to get an alignment, ask for the printout - UP FRONT. Also, UPFRONT, tell them you want to know if anything is out of spec and that you are willing to pay for the eccentric bolt or camber plate, but you need to know how much that is going to cost BEFORE you approve them.
Be aware that many alignment techs think that if the alignment didn't come adjustable from the factory, then they can't or shouldn't adjust it. They are wrong. That's where the eccentric bolt/camber plate comes in.
Further, my experience says that in order to get good tire wear, the alignment has to be within the inner half of the spec - that is, the published tolerances are too wide, by half. Plus I am of the opinion that any camber over 1° is too much for good tire wear.
Third, hopefully you'll wear enough of a new pattern in the offending tires such that it will eventually disguise the vibration. Ya' see, the wear pattern developed an "Out of Round" condition, as well as a balance issue. Balancing the tires is only going to fix part of the problem.
Good Luck!
