BBBRPDL,
Unfortunately, I really don't have the experience to recommend an axle for someone your size, mostly because I really don't know what's available. I weigh 225-lbs. My closest experience is as part of a 350-lb tandem team. I'm speculating, but I suspect steel axles will be part of your recipe, as well as plenty of spokes. Heck, I think tandem wheels with 40-spokes would be good. But I don't think they can be had in 135mm hub widths. Hopefully, someone here will educate us all.
Good Luck,
Scott