I’ve tried to get samples for a very small “green roof” garden demonstration that i was putting together, but never got to because the plants died (not enough sun on my back porch). I would find a local supplier and call them. I’ve found they usually will not ship small amounts specially mixed for you, but if they are working a job and have some left over, they sometimes will just give it to you. You likely will have to go pick it up, though. Also, if you go to a trade show and see a medium supplier, ask them what they are doing with the mix after the show, and you would be interested in the stuff if they are getting rid of the samples (not the box, just the mix). Often, they just discard the mix instead of shipping or hauling it back to the office. You should think ahead and bring a few heavy duty bags or keep something in the car when you go to a show.