Wheels:

You have seen those jogger/walkers all over, you know the kind with three wheels and some sort of
nylon bag support with a sun shade over the top. In our neighborhood the homeless guys have started turning them into trailers for their stuff. Well I had a couple in my yard and finally took a good look at the rear wheels; it ends up that the plastic locking brake and all the trim pieces come off to leave a hub that takes a simple bearing, in my case I just salvaged the bearings that came with. In my case, the bearings fit a 1/2" bolt, or spindle.  If you need different bearings, these can be pretty cheap, I have seen them called: insert bearings, flange bearings, wheel barrow bearings. These wheels measure 10"and 12", and i cant really testify to how these will work, but they show promise, and they are FREE.