Israel maintains a naval blockade, as a result the Gaza City port is restricted to fishing boats. And search. Local manufacture, the make their own rockets, still requires raw materials. I don’t know if they’re making fertilizer explosives, but they’d have to import the fertilizer and fuel oil. I have to think the bulk comes in through the tunnels to the Sinai.
That is my understanding too. Most of the actual weapons were smuggled in through the tunnels via Egypt.
What I have read is that Iran loads a ship. The ship goes to Yemen and then to Somolia. The weapons are then loaded on a truck. Then brought to the Sinai where they are unloaded and brought by hand into Gaza through the tunnels.
The Egyptian’s could stop them IF they really wanted or at least most of them. However, they do not. So, that means someone is getting PAID to look the other way. It is not just some poor Egyptian Army Border guard either. They may get a small cut. The Egyptian generals are getting paid by Iran to let the weapons flow.