I don't know where you can get your samples. Maybe someone else can tell you that. You didn't say what you want to do with them but there are 2 ways you can preserve them. One is the pressed method--your phone book method may work but you would have to put something absorbant on each side of the flower and add extra weight. Another way is to preserve them using silica jell. There are better experts than I am, on the web with step by step instructions. Google how to press flowers and How to preserve flowers in the microwave.

Wow, I am surprised that there is interest in this thread, I had posted this ten years ago! I took a break from this site for years, but I am back with a slightly different screen name. I am still growing many of the double flowered trillium. It is my understanding that it is against the rules to be selling any plant material here on GardenWeb, and when this was originally posted ten years ago it brought out a number of people that thought because I was growing so many of these that I would agree to trade it for something that I had no interest in, or that I would just send them some because I had so many. That was a learning experience for me! Here in Ohio bagged Fafard soil mixes are still available, I don't remember which exact mix I used for pot culture, but it was one formulated for containerized perennial plants. Trillium would probably do well in any soil mix that has a percentage of fine bark in it, and one that drains well. Over the winter I would "trench" my potted trillium burying the pots in the ground just under the rim of the pot. It has been my experience that rodents have no interest in their rhizomes, there is a large population of voles and chipmunks here that have never ever bothered any of my trillium. It is the deer you have to watch out for - I think they can smell trillium for miles and are attracted to it like a magnet once it is producing leaves and flowers. Last spring I had deer eat a section of my trillium bed down to the ground and will put up fencing this year as soon as I see them starting to grow. They don't usually show any signs of growth above the ground until the beginning of April here, so don't despair, it is still early in the season. Be patient and they will grow for you. Here are pictures of my trillium bed last spring, this is Phlox divaricata 'Blue Moon' that blooms at the same time and is a nice companion plant.

I have a large patch of established trillium and they self seed like crazy. I have found the seedlings have shallow roots and are actually quite easy to transplant despite their reputation. They definitely prefer rich soil and dry shade. Trillium seedlings develop slowly and they look different each of the first three years. The first year seedlings have two linear leaves and that is it. They go dormant about July in my climate and I think a lot of people mistakenly think they have have killed them when they do that because the adult plants don't die back that early. The second year seedlings have one heart-shaped leaf that also dies back in July. The third year seedling has the tripartite leaf and may or may not flower. The fourth (or fifth) year plants look just like the third year plants, but they will generally flower. They don't die back until October or November, when the full-size adult plants also go dormant. Since you ask about encouraging it, you could try a very dilute solution of an acid plant food. I did that one year and my trilliums got huge. Be careful not to over do it. I would use about a 25% solution and I would not apply it more than once. I don't leave much leaf litter. I clean up most of the leaves in the fall, but I do mulch a lot with compost in fall and spring if I have the time.

Martha, I have not had much success (some) although they readily seed out in the woodlands. I know they are to be planted fresh. I keep trying, so if nobody has asked for the seeds, I would be glad to experiment again. Let me know, and I can send my mailing address off list. Have been traveling but also have not been active on this site much anymore. I have to admit doing more on Face Book.