Hello!
I have a list somewhere. Off the top of my head milkweed fluff, milkweed ovum, mullein pith, goldenrod pith, sunflower pith, punkwood, chaga, amadou (trauma layer of Hoof Fungus or Artists Conk), sycamore fluff (seed balls). I think thistle fluff was as well but do not recall if it was Canada, Bull, or both. Both work well in char mixes. Char mixes are what I call the Native American (especially the Inuit) technique of mixing uncharred materials with charred. I typically use 1/3 char, the rest uncharred. Fungi, punkwood, plant fluffs, etc are great candidates for the uncharred portion. Fluffs in particular work very well.
The key to using most NUTs (Natural Uncharred Tinders) is micro-charring. The first sparks to land char a tiny spot then fizzle out. The next spark to land on that char can grow enough to be sustainable and be brought to flame. Similar to how we char an area at least dime sized before going for an ember with a magnifying lens. Much higher rate of success. Or how we char the edge when using a Tinder Tube. One should expect a lot of striking when working with NUTs. While most chars will produce an ember in less than thirty strikes, NUTs may require up to 300 strikes.
No, most NUTs are never going to replace chars. But it is pretty fun to challenge oneself to start a fire by bringing only a piece of metal such as a knife, hacksaw blade, shovel, etc along. Also, NUTs solve the "First Fire" problem. Which is: "How do you make char when you do not have a fire?" In this article (with a video), Paul from Jungle Craft in Malaysia goes over just how robust of an ignition method F&S can be in the hands of the skilled. I have been doing everything he does in that video here in the Upper MidWest for years.
http://www.junglecraft.com.my/index.php/advanced-flint-and-steel/
Punkwood can be found anywhere wood is. Boxwood Elder and Eastern Cottonwood are the ones I look for first. Several others have worked. They keys are learning when it is at just the right stage of decomposition (same as for Friction Fire) and cutting into wedges. Thin edges catch sparks the easiest, but often fail to generate enough heat to sustain themselves. Thick edges catch sparks poorly but when they do, the ember can be grown. I have found wedges to be the best of both worlds.
What tinders can be found in your area I cannot say. All you can do is what I did: have fun experimenting with them!! Some I had heard about, some I just decided to try. All required much experimentation to reach the point where I feel confident about finding and using them.
The edge geometry of the rock plays the biggest part in where sparks are thrown. That being said, generally more sparks go up when striking the rock with the steel and more are thrown down when reversed.
How I strike depends on the tinder I'm working with. Things that hold together well like charred cloth, charred mullein leaves, wedges of charred or uncharred punkwood, wedges of charred or uncharred chaga, charred or uncharred amadou, etc can be set on top of the rock.
Things that do not hold together well like charred cattail fluff, charred grass, charred (not punky) wood, char mixes, charred or uncharred dusts, etc are better off in a pile, tin, etc. For them I typically hold the steel above the pile at a 45° angle and strike it with the rock. The angle allows the follow through to pass above the pile without disturbing it, unlike holding it vertically (90°). With a little aiming, just as many sparks land on the pile with either the 45° or 90° hold.
Hope that helps. Happy Trails!!