I think the roadside co is called axle dr they’ve replaced one for me but it got to the point it was cheaper replacing axles . I would Repack bearings every 15k miles , these were commercial use . Anything over 15k and I would start hucking things down the road . I always kept a 1 inch dye in my toolbox for a bearing issue , you could cut and rethread it a few times . At least gets you off the side of the road . Not a long term option but a cheap tool to keep and could save some hassle . It’s called hwy robbery for a reason.
How hard would it be to make up bolt on spindles? A male spindle with a stub which slides into a female extension welded on the axle with the requisite amount of overlap and a pair of plates which are bolted together. I would think it should be fairly easy and sufficiently strong if done by a qualified welder. Seems like an interesting engineering problem.
I started thinking about that myself. I've got the tools to do it. It just becomes a question of "how much do I want to make my own parts supply for my trailer". I think I'd rather just convert to Dexter's replaceable-spindle torsion axles and be done with it, if I went that route.
Lots of torsion axles have bolt on spindles. They use the same 1' castle nut and cotter pin on both ends.
Would make more sense to me to buy a spare axle and carry it than to worry about modifying to a replaceable snout… We broke a axle in West BF California a few years ago, made a crappy drive home a day longer…