For those looking for a 240 rear wheel, I just posted a link to a factory 240 rear in the random items for sale section. I have no affiliation with the seller and know nothing about the wheel.
For the Gen I's, I have a wheel for-sale, 5-1/2" X 18 " which is much-closer to the OEM height of the wheel/tire, so you don't lose as-much top-end as you do whan going to a 17" rear wheel/tire. Not-cheap. Running a much-wider rear tire may require you to notch your swingarm.