What materials and skills are available?
Currently bags are bought in Nairobi, though it is possible to buy backpacks of adequate quality in Mtoti Andei. The materials are available in Nairobi - for the bag itself, the straps, zips, pockets. There are sewing workshops in Mtoti Andei, so it would be feasible for them to be made locally if required. Jeremiah is convinced that the local seamstresses/tailors have all the necessary skills. They certainly have manually operated sewing machines capable of sewing the thickness of canvas used in the current bags.
If it was necessary to construct supports for panniers, then metals are also available locally. Right angle, square, round metals of all thicknesses can be bought in the market in Mtoti and the local artisans are capable of making quite complicated fixtures. Nuts, bolts, tubes, supports are all sold in the local market. Small repair kits are also available there.