How did they get Israeli Defense Force uniforms?
Maybe from the IDF prisoners they took...
Or they manufactured them... it's not hard to find photos...
Perhaps they bought them on the black market, or Arabs within the IDF smuggled them out.
Many possibilities.
It's cloth. It's easy to copy cloth.
I would imagine they made them. Or they could have had agents inside Israel steal them. Since a great percentage of Israelis are reserve members of the IDF (Like Switzerland, Israel doesn't so much have an Army as it is and Army), there are likely plenty of them about. I don't know if they have the same sort of military surplus stores we have, but around here it wouldn't be difficult to come up with many full sets of US military BDUs, in Woodland or Desert camo patterns.
Or else they've been stealing laundry