[Arran]

The model 70 cathedral should be totally manageable, fleabay has at least 1/2 dozen of those listed every week. Even the model 90 cathedral should not be too hard to find, especially the version with the single #47 output tube. In keeping with the chair-side theme you could look for one of the ones with a 70 or 71 chassis in it, that would fill the console and and chair-side quota at the same time.
The 15X sets do seem to turn up on there at least once a month or so, but finding one within driving distance is the issue. The 15DX may be a different story, the sales figures were at least 10:1 in favor of of the 15X over the 15DX.
As for the 38-690, that may be a tough one, but they do seem to turn up when you least expect it.
Regards
Arran