They look to be good over engineered wheels that were once commonplace, but no longer so.
If I found NOS ones, I'd be loathe to fit them on unless the mower was going to be a static exhibit.
What's wrong with the existing wheels? Could you clean them up and maybe even grind the tyres back with abrasives to renew their appearance? People do that.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!