A couple of the (many) windows in our house are missing either the
screen or the storm in the triple track attached storm windows. The
triple tracks are old and eventually need to be replaced so I don't
want to spend a lot of money on custom replacements and since they are
quite old I can't identify the original manufacturer.

Short of replacing the entire triple track now, are there generic
replacements that I could assemble/build to my exact height/width
dimensions? If so, where could I get them?