Hamas has started in on the 7th of october 2023, effectively rolling back years of negotiations done by Yasser Arafat. Where do you think they've got the weapons from? Netanyahu is no better, but they offered him the perfect motive for a response.
Ultimately, from the United States taxpayer. Who supply the Egyptian military government, who turn a small proportion over to the Islamists to keep them from too much rabble-rousing. Who smuggle them to Hamas.
Both Qatar and Iran supply money and other forms of support to Hamas. But no RPG makes it into Gaza (across a shorter than 10 mile border) without the Egyptian military sort of knowing about it.
https://www.fdd.org/analysis/2023/10/19/hamas-used-iranian-p...