You had to get your trailer towed back home, but you still went camping!
I'm not sure that a bigger axle will reduce the risk of failure or not. If the bearing isn't greased properly, installed incorrectly, etc, it could still fail. I don't think it would hurt though. My only thought on this however is that the camber of the tire may be slightly different with a 5000# axle since it would be bent to achieve proper camber at a larger load than the 3500# axle. Maybe not a big enough difference for any impact, just a thought I had. 3500 to 5000 isn't a huge jump.
The torsion axle may cause the trailer to sit lower, so consider installing it on spacers between the axle and frame to ensure you get enough ground clearance for stabs, dump valves, etc.
The manufactures that come to mind are Lippert and Dexter. Not sure, but you might be able to buy it complete with hubs and brakes too.