They don't need them.
Stop selling spare parts and they will soon be useless.
They are incredibly maintenance intense even in peace time. In wartime even more so because even minor combat damage adds up.
Iran bought 79 F-14 in 1974. Revolution and arms embargo 1979. In 1984 they had 15 airworthy planes kept in shape by taking parts from other F-14s.
They have since got some spare parts from hostage deals and the black market. Probably reverse engineering too so they have about 40 of them flyable. But the 5 first year has 80% of the fleet grounded should say something about it.
A minority of the population benefits from an autocracy.
And/or they will be seen as traitors to whatever comes to power after the autocrat.