For autocross, I haven't had a problem with replacing the ball bearing types. I have the standard replacements, and for autocrossing, as long as they're changed periodically (when the slop gets to be a bit too much) they're OK. They're not great, but they do for limited abuse. They're what I believe are called "Conrad" style bearings. The aforementioned bearings with more balls in them are (if I'm not mistaken) called something different, but they cross-list if you call a bearing company. They're more expensive (about double) but they provide additional support. They may still have too much play to prevent some axle twisting, but they'll bear the load better for a longer time without degrading and initiating an immediate failure.