I'm not sure exactly who they buy them from now, but prior to 2001 they were getting their weapons from Pakistan who was buying them from both China and the United States. I would guess that not much has changed since then.
They certainly are not getting them from any of the other countries in the region as all of them are very anti-Taliban. Iran and Uzbekistan were both major supporters of the Northern Alliance and are both major supporters of the new government. And China certainly is not giving arms to Islamic extremists as they have their own problem with these extremists in their Xinjiang provence.
Here is an article about a recent weapons find by Canadian troops:
http://ottsun.canoe.ca/News/National...33447-sun.html
No mention of the origin of the weapons. I'm guessing they are American-made. If they were from some place like Iran or China, you can bet our politicians and media would make a big fuss over it.