I don't know about others, but a good source for "tufts" and tall grass are the "chip-brushes" as shown below. They are meant to be disposable one-time use brushes and made cheap. I use about five or six dozen a year somehow. They cost between 65 cents and a dollar plus at the hardware store. I wait until there is a big sale and buy about six dozen of various sizes.
You can make your own tufts and lines of tall grass easily with these.
One technique is the lay down a heavy bead of white glue on the bristles, say about 1/2 inch from the end of the bristles and let it soak through (I apply several layers from both sides, and dry. Then cut through the dried glue. You basically have one big "tuft" of yellow tall grass: cut it into small pieces as you want, etc.
However, I just put down a big drop of white glue and then cut some bristles and stick them into it. Takes more practices than you would think to get good at inserting the bristles into the glue-drop so they look good, but you learn.
You can dye the bristles anywhere from light green to dark to brown. diluted water-based paint works best.