Wheel bearings are relatively easy to change. In your situation, a custom axle may have to be made if you can't find bearings to fit the wheels mentioned.
www.goallballs.com
is one place I've bought bearings through.
Old bearings can be removed by driving them out, a propane torch can be used to carefully expand the wheel hubs, and then use a hammer and punch to drive the bearing out(moving the punch around the entire bearing, so it won't bind up).Check for snap rings, as some Kawasaki's have them as a safety retainer for the bearings
When getting ready to install the new bearing(s), put them in a freezer for an hour or so, as the bearing(s) will slightly shrink in size. If the hub is warm, the bearing may almost drop in, perhaps needing a slight tap with a block of wood to seat it.
Never hit the inner part of the wheel bearing, as it may damage the race, always apply force on the outer part of the bearing. A large socket that fits the outer race works best.
