Well, I certainly do not have a magic ready-made solution for you. However, when I was faced with the same problem...credible observation platform railing...albeit in HO for a Santa Fe heavyweight car, my solution was to scratch build the railing. An interesting project....done years ago when the eyes were sharper and hands steadier!
For your modern obs in O scale with horizontal bars, I would suggest looking at iron bar fencing from various manufacturers and in different scales depending on the scale proportions of the railing you're replicating. For instance, it may be that, say, a Grandt Line plastic iron bar railing in HO might have bar lengths and spacing already tied to carrier straps which could then be incorporated into railing posts/walls/etc. A bit of judicious trimming here and there and, as Si would say, 'Hey! That looks good enough to me, Jack!'
If you trace the floor perimeter onto a piece of cardstock, fastened to a board, overlayed with a sheet of waxed paper, you can build your railing structure off-car, paint it (Silver? Tamiya's spray TS-30 Silver Leaf is my favorite!), install it.
I just noticed that Keil Line (direct or Walthers) sells a vertical bar tailgate (O scale)for passenger cars, p/n 48104. That would be a white metal casting. Without a picture (none on Walthers' website, unfortunately) I can't say whether, turned on its side, the bars might give you what you're looking for. Personally, I'd rather scratch something like this from plastic (styrene or ABS) that metal. I know there are brass artisans out there...even a couple of forumites!...who are far more skilled in brass fabrication than I.
Sort of a hit-or-miss bunch of suggestions, I know. If you posted/referenced a photo of the prototype railing you're trying to replicate, I might be able to do better.
In the meantime, FWIW....
Sounds to me like a fun challenge!!!
KD
