There was a company called MBS out of Japan that used to make tapered wheel bearings for the 3600, 3800, 4100 trucks. I actually bought a set. I don't believe they're available anymore. They were beefy and well made, but I did have some fitment issues.
One of the problems is the seal rides on the inner bearing. The inner sleeve of the bearing is extended. You can find a bearing with the same inner and outer dimensions, but you'll need a machined sleeve for proper spacing and for the seal to ride on.
The next issue is the outer bearing. It's an odd size, .908 ID, if I recall. You'll never find a tapered bearing that diameter. You're only option is to have the spindle machined to accept a more standard size.
Anyhow, you're better off sticking with the B45, B46 ball bearings. They're plenty stout and more than capable of anything you throw at them.
