Finding an original Westinghouse boot will not be easy, alas. But you never know - I think a couple of them turned up in the Shopper's Square forum earlier this year (original ones, still in the box!!)
Have a look at some of the restoration threads here on the site for ideas on how to substitute more recent door boots; IIRC there was an older Kenmore or Frigidaire boot that fit, but I fear that these parts may now also be NLA.
Where's the fella who was looking into having some new ones made? I'll go out on a limb here, but I think there's some potential demand from us Westy Laundromat owners.