Trillium from seed
There are a few forms of Trillium's for sale in Australia but not many, so seed raising is the way to go.
I find the seed germinates best when sown in pots with a fine gravel over the top and put out in the rain, in a shady position and do not dry out in the summer or that will be the end of them, up out of the way of slugs and snails as they love their leaves. They take 4 to 5 years to flower from seed if they are fed from the minute they first germinate, I use a granular fertiliser sparingly. I then pot them on in their 2nd or 3rd year into a good potting mix with leaf mulch mixed through it. Moist packed seed is the best as it germinates much faster than seed that has been dried out. I have recently found a person in the US who packages and sells fresh moist seed through the Scottish Rock Garden Forum, and I will let you know when she has seed available. There is a lot more effort in selling moist seed as it can go mouldy, you need to keep it refrigerated and just the right amount of moisture.
I was taught to keep all my Trillium seed in a jar with a lid as it can be smelly, in the refrigerator with the pulp around it, to help in germination, sow as soon as you can. European wasps steal the seed as soon as it is ripe, so your need to watch for ripe seed every day, the pods will twist off easily when they are ripe, or cover the seed pod with a muslin bag.
Trillium chloropetalum in a woodland setting in my old garden, with Erythronium, Paris, Epimedium Hot Lips and a white flowering Japanese Primula kisoana.
Trillium chloropetalum yellow flowers below and above from New Zealand seed.
Trillium cuneatum NZ seed, with Pachyphragma macrophyllum and the blue flowers of Brunnera macrophylla Langtrees. (Below)
Trillium cuneatum NZ seed (Below)
Trillium erectum album (Below)
Trillium flexipes (Below)
Trillium flexipes pink (Below)
Trillium flexipes with a red edge (Below)
Trillium grandiflorum above and below, top Photo was taken at Sissinghurst and the one below is my form with wider petals to the flowers.
Trillium grandiflorum Rosea from Archibald seed and another variation in petal shape again of Trillium grandiflorum in the back ground.
Trillium luteum raised by an old friend Phyll Bear no longer with us but her plant is (Below)
Trillium maculatum (Below) in the glass house.
Trillium pusillum Var. Ozarkanum with dark leaves and stems to the flowers.(Below)
New Zealand seed.
Trillium recurvatum (Below) UK seed.
Trillium sessile the true form imported from New Zealand from Stewart Preston. (Below)
Trillium sulcatum NZ seed (Below)
Trillium vaseyi with a mark on the flower but has never produced that mark again. (Below)
Trillium rivale Purple Heart. (Below)
Trillium rivale with all their variations (Below) Aaron's with some of my dark leaf marking's.
Trillium rivale maroon leaf, does not always germinate with the dark leaf (Below)
Trillium rivale a double flower that has never flowered again as a double (Below)
Trillium rivale Archibald seed Dark Form 1920 520 (Below) 2001
Two books I recommend are Trilliums for Your Garden by E. Gay Henderson full of practical advise, and Trilliums by Frederick W. Case and Roberta B Case.