Thanks for your suggestion, burdar. I'll tell you what I discovered.
The brake pedal bushings are apparently Chrysler part no. 2467770, and appear to be available from some of the usual online Mopar parts suppliers.
I can make an exact duplicate of the steering column-to-cowl gasket from gasket material, so that is not really a problem. It won't be made of that white foam stuff like the original, but I don't care.
I still haven't found a source for the steering column "O" ring, but my local hardware store has a pretty good selection of large "O" rings and I think they might have one similar to it. If not, I am pretty sure that McMaster-Carr or Grainger would have one.
Thanks again, everybody.