This accident has indeed nothing to do with spare parts.
Getting spare parts for Iran airlines Western types is a problem, a difficult and costly one but they get them eventually. Getting western airframes second hand is not a problem . Plenty on muslim countries selling to them .
Last time I was in THR ( last year) we visited HESA and went inside one of their 140. It is assembled in Iran, but it is a basic version. I was told only the Government uses them. Only 5 or 6 were assembled and flying.
All commercial airlines in Iran has since a couple of years dropped all their Russian/soviet types. Maybe during high demand one can be leased in , but it is ( was until then at least) exeptional.