Did Promaster quit "making" lenses
Promaster never made any of their own lenses (as far as I could determine).
What they did do, was rebadge 3rd party lenses (usually Tokina or Tamron) as "Promaster". The big diffrence was that Promaster offered a lifetime lens warranty :
"Photographic Research Organization Inc. (PROMASTER) warrants that your PROMASTER Spectrum 7 Lens, purchased AFTER 1/1/2000, will be free from defects in materials and workmanship for as long as the product is owned by the original purchaser."