You might try contacting the Geology Department in the nearest college or university and ask where the nearest place to you might be. Once you find an accessable area of interest, walk along creek beds and look for the chunks of chert. Take along a hammer and
wear safety glasses. When you see a likely candidate, knock off a piece and see if it looks like chert. Once you find it, take it home and let it dry in your garage or basement for several days. Then build a fire and toss the chunks of chert into the fire and burn it for an hour or so to prepare it to knapp. You will also need a "hammer stone". Don't burn it. Your hammer stone needs to be about the size my grandmother used to call her big biscuits "cat head" size, and fairly rounded. You will use the hammer stone to knock off chips from your large burned nodules. Again, let me reinterate that
you must use safety glasses because when you are knapping, bits of the stone will fly everywhere and these pieces are sharp as glass. One tiny piece in your eye can be devistating.
I am fortunate in that we have chert laying all around on the ground here in the Texas Hill Country. I am still trying to learn to make my own gun flints. I have managed to make quite a pile of flakes and actually made a couple of usable gun flints. The learning process goes on and on.
When you are through with your knappig for the day, be sure to sweep up all of the bits and pieces of chert. They are like tiny razors and will cut you if you or someone happens to step on them barefoot.
Sorry for the rambling. I think I answered your question in my first sentence and the rest was just rambling.
BTW, Dixie Gun Works sells flint nodules but unless you can go by and pick it up, the postage will eat you up.