You need to collect moss from a site similar to your patio's exposure. Moss grows where it can out-complete other greenery that can grow under the same sun/climate/water supply conditions. That means a very thin soil layer, like where soil has washed onto the pavement at the edges of parking lots. Taller plants can't grow in such thin substrates, and the seeds that can root in good moss sites die pretty quickIy when it dries out. Moss needs a little more moisture than is typically available in such a situation, too, so look for a location that is at the bottom of a slight slope, like the edges of a parking lot. Moss needs some shade, too, so a site adjacent to a fence, building, line of trees, or anything else that runs north to south which provides half day shade is necessary. East to west doesn't work because the south side is too sunny and the north side is sunless.
So, on either side of a north/south fence where soil has washed onto the pavement that is pitched to the edge of a parking lot of a closed factory where the lot has not been maintained, especially not snow-plowed for a number of years is the creme de la creme site.
