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.
In hindsight, my question was dumb. ;/
One FReeper even posted a link where you can buy IDF uniforms online!
Its not hard to imagine the evil uses Hezbos would come up with by impersonating the IDF, and you know Al Jazeera and the regular media would lap it up without question.