I was lucky to pick up a Marlin 336ER a few years back and like it very much (but I'm a big fan of 35 cal in general). For me, it is an excellent companion to my Marlin 1894c in 357 Magnum. I had no trouble finding brass or dies. I haven't hunted with the rifle yet, just shot it at the range, but I'm getting it ready for next year's use. The rifle is currently sporting a Williams peep, but I'm going to be scoping it to take advantage of the longer range possible with the round --- I'm currently debating whether to go with a Leupold VX2 2-7x33 or M8 Compact 4x. My current leaning is towards the 4x to keep things simple.
I'll be mounting the scope this weekend so will be sure to post some pictures. I'm currently loading the rifle with Speer's 220gr FP, which is a great bullet and has one of the higher BCs for lever-suitable 35 cal bullets. My next experiments are going to be with the Speer 180gr and some of my cast moulds. I'm hopeful that a Lyman 225gr Keith will work well. The nice thing about the 356 is that with the proper lube, you don't have to sacrifice velocity to shoot cast.
BTW I know you've had the WTB for a while, but keep your hopes up. Since I bought mine, I've seen one or two others listed... not on the EE but elsewhere.