Early man searched far and wide for quality lithic (stone) material to make tools. We see evidence of its value in the extent they went to obtain it. Early archaeologists found nearly 300 excavated pits, to obtain the Nebraska nehawka flint sources, some over 10 feet deep. This was done with primitive digging implements! Good stone was a trade commodity, and carried hundreds of miles from its source. One of the qualities they looked for was that it would form a sharp edge when it fractured. Often the flake resembled a shell. We call this a 'discoidial fracture.' The dark dacite, upper left, shows where this type of flake was removed. Another aspect was that it is 'homogenious'. Basically, that it is uniformly the same material throughout. You can see this in the stone pictured. Clockwise from the upper left you have: dacite, nehawka flint, keokuk burlington, obsidian, Fort Payne chert, novaculite chert, and republican river jasper. Glass is a good example of the qualities you would like in knappable stone. In fact, some flintknappers regularly flake some fine points and blades from colored glass. Some lithic material is easier to work than others. An example of that would be obsidian, dacite, heat-treated novaculite and burlington. I mention heat treating. Some stone, to really be workable needs to be slowly heated. This changes the crystalline structure in some way as to make difficult stone glossier, fracture to a sharper edge, and require less force to knap. Early man may have done this periodically, by placing spalls in a layer of sand, under the camp fire. Nowadays kilns are used. Where can you find lithic material to knap? Probably, the easiest recommendation is to use an internet search for flintknapping suppliers, or possible upcoming Knap-In events. Vendors will have instruction material, tools, and appropriate rock. One vendor I like, in my personal opinion, is Craig Ratzat at http://www.neolithics.com/ . At local rock shops I would really only look for obsidian. If you are fortunate enough to live in area that has rock you may be able to locate outcroppings by internet searches, inquiring local rock clubs, or searching road cuts or ravines. Some archery clubs have members who knap their own stone points and would be sources of information and instruction.