Old shower does not have standard seat or stem. Need replacements instead of replacing the whole thing. Can't afford it right now.

Home Depot or Lowe's' is as good a place as any. Even plumbing supply houses don't carry as much of the old stuff as they use to. Show picture of valve.

I suggest you go to an old, neighborhood plumbing store. Usually, they carry replacement parts for old or discontinued plumbing fixtures.

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Milo