Afghanistan. The border region between Afghanistan and Pakistan - the "Northwest Frontier" of the British Raj - has been awash in weapons for centuries. Many of the weapons have been improvised. In fact, for several hundred years, many of the weapons used have been made in village workshops, laboriously hand-made copies of up-to-date Western equipment. Traditionally, village craftsmen secure a sample of a modern firearm and in short order have a reasonable accurate facsimile in production. The production of facsimile weapons has been a thriving small industry for generations, with specialized knowledge of how to make a particular weapon, or just a particular part of a weapon, handed down from father to son. In some areas of the frontier zone the production of arms is a significant industry; for example, the Pakistani village of Darra (about 40 miles from the Afghan frontier - http://www.ease.com/~randyj/pakfoto1.htm), is practically a shopping mall for handmade arms, with over 100 tiny shops selling weapons, including RGPs, artillery rounds, and, reportedly, even the occasional tank.
Mostly these shops sell the products of local workshops that turn out pistols, rifles, and even automatic weapons, including heavy machine guns. Methods and tools are usually primitive, but used with great skill and much patience. The resulting arms are meticulous reproductions of the originals, often down to the serial numbers, and have similar performance characteristics. The only significant difference in in their durability; they are usually made from inferior materials (e.g., rifle barrels are often fabricated from rebar), and thus wear out relatively quickly. Currently, the most common weapon produced in the local factories is the AK-47, either the Russian or the Chinese versions, but other weapons can be had as well, such as a pretty good reproduction of the old British officer's sidearm, the .32 caliber Webley pistol, as well as other British weapons, some American arms, and even a local version of the Israeli Uzi. Prices are relatively low; a Darra made AK-47 sells for about $250, while ammo usually runs a dollar a round. The British found the frontier tribesmen so skilled at reproducing weapons that during the later decades of the Raj (1920s-1940s), they were very careful to keep mortars away from the Northwest Frontier Province, lest one be captured.
This enormous skill in making firearms is one reason for the extensive use of improvised weapons by the Taliban in Afghanistan. Aside from IEDs - improvised explosive devices - fabricated from old artillery shells or demolition munitions, "homemade" landmines have long been produced in the region (introduced by the British in a moment of forgetfulness some 80 years ago).
Although none have yet been encountered in the field, local weapons smiths are rumored to have developed an improvised anti-aircraft system using old Soviet 107-mm surface-to-surface rockets. The 107mm is not intended for use against aircraft. Reportedly, local weaponeers have been experimenting with substituting for the 107's standard fuze, an impact device, fuzes from old Soviet 23-mm to 57-mm anti-aircraft artillery rounds. These fuzes have a self-destruct feature. Hypothetically, 107mm rockets, with these fuzes attached, might be used in volleys to fill the air with shrapnel. On paper, this looks like it could work. In practice likely to prove little more than a nuisance, in certain tactical situations the improvisation might be quite effective.