I don't know of a source for replacement handrails made specifically for the P2K tank. But in general, I find that plastic tank-car handrails (like plastic sill steps) don't long survive contact with my three left elbows and two right thumbs. In my hands, wire handrails are far more durable. To replace the P2K handrail you'll need handrails and joiners and stanchions. Precision Scale #32110 stanchions are beautiful; for handrails, I've been using .015" OD phosphor-bronze wire (PB holds its shape better than brass), joined with .016" ID plastic tubing from smallparts.com. Tony Thompson points out that my handrail is really too light: should be .019" OD. I don't know of a source of .019" PB wire, but Tichy supplies .020"; if I can find .021" ID tubing, I'll try it. The stanchions will need to be drilled to accept wire that large.
Ted Culotta uses a related technique, described in one of his RMC articles: joins handrails with *steel* tubing, cut with a cut-off disc in a Dremel tool. (If the tube is steel it needn't fit quite so tightly on the handrail.) I lack Ted's skill with a Dremel, have tried it and failed. Others think it isn't a big deal, though.
Al Brown, Melbourne, Fla.