The Vietcong got weapons and supplies from China and Cambodia, the Afghani insurgents got weapons and supplies from the US to fight the Soviets (including explosives ), and the current Iraqi insurgents get money and supplies from extremists all over the place, mostly from the Emirates (afaik).
All of these fighters did not build their own weapons and skills out of nothing.
 "Other CIA specialists and military officers supplied secure communications gear and trained Pakistani instructors on how to use it. Experts on psychological warfare brought propaganda and books. Demolitions experts gave instructions on the explosives needed to destroy key targets such as bridges, tunnels and fuel depots. They also supplied chemical and electronic timing devices and remote control switches for delayed bombs and rockets that could be shot without a mujaheddin rebel present at the firing site. " http://msuweb.montclair.edu/~furrg/pol/wtc/oblnus091401.html
And while those armies did eventually get arms supplies from abroad, in their early days they had to improvise. Viet Cong fighters early in that war, for instance, had to scrounge old French weapons or even homemade shotguns fashioned from galvanized pipe. The Iraqis' first IEDs were jerry-rigged artillery shells lifted from abandoned army depots. The foreign arms pipelines generally don't open up for a revolutionary army until it's proven it can fight and win at a small scale on its own.