Actually I think my grandmother invented the masking tape trick, I use it all the time, learned it from her.
For leather I use mainly old purses, the leather comes in great thicknesses from those, certain parts of the purse are thick leather, others are thin, and you can get an old purse for about 1.50 and if you pick one with a woven or braided strap you get a nice load of long leather lacing to use. The other plus is you can get wild colors like red, green and yellow, or any color of leather in a purse. From a medium/large size purse I can make about 10 pouches for 1.50. Just go to a thrift store and find a bin of purses, one of them has got to be leather, but be careful, leatherette is decieving sometimes and they will throw in say tassles made of real leather and then leatherette for the rest. The problem with leather coats is that they are often of thin leather. I also have used the bottoms of knapsacks, and you can get a little leather off of the palm of a workmitt, you can even buy those at the dollar store and get 2 or so pouches out of them if you get a good pair, and if you know a taylor you can buy leather knee and elbow patches.
And no matter where you are you can always go yardsaling on friday and saturday (especially saturday,) and get purses, jackets, backpacks, boots, belts, etc. that way. With a couple wide belts you can cut enough strips to braid an entire sling.