I haven't seen such a forum. But maybe the Exchange forum might be the place to ask if there are any trees/cuttings going! Don't plant a female tree near the house though. They smell like cats urine when in flower!!! Best to ask for a male tree.

My understanding is that willow is uniquely suited to that kind of propogation, definitely not the norm for trees. Ginkgo can be grown from tip cuttings but if you want a more mature tree you'll have to buy one potted or bare rooted. It won't be cheap, we paid $50 for ours, about 5 ft tall.

Here is a link that might be useful: propogation of Ginkgo biloba

you can find information on Ginkgo biloba at:
http://www.healthvsdisease.com

Here is a link that might be useful: Health Information, Diseases and Conditions, Diet and Nutrition

To propagate by seed, gather the seeds in autumn. Remove the fleshy coating by placing the seeds in warm water, crush the coat and squeeze the seed out. Rinse several times and dry well. For best results, refrigerate the seeds for 2 months before sowing, or chip the seeds with a sharp knife, or rub them lightly over sandpaper, then soak the seeds in water for 24 hours. Another method is to store the seed at 21C for 2 months, then at 4C for 2 months, then soak for 24 hours. Lightly cover the seed, and keep soil at 18-21C. Seed will usually germinate within 30-60 days. Sow in a sandy loam about 1.5cm deep. Cover lightly with sand, leave in a well-lit place (not full sun) and keep soil moist but not wet. After germination, never allow the roots to dry out or to stand in water. Germination takes 30-60 days at an ideal temperature of 23-24C, and is irregular. To be sure of the sex of your tree, take cuttings of young or half-ripe wood about 15cm long, in summer. Keep them moist. They usually start growing best in their second year. Cuttings may be grafted onto opposite sex trees. Prefers temperate climates with moist soil, full sun and high humidity. Tolerates a wide range of soil acidity levels. When male and female trees are grown together, the female produces yellow plum-like fruits in autumn, which, when ripe, look like small brains. When these fall to the ground and are trodden on, they exude a foul odour like that of vomit or rancid butter. Trees begin to reproduce when they are about 20 years old. The seed inside can be initially, but grows faster as it ages. They are cold hardy to Â30C. To distinguish the sex of a tree, the female trees are said to have less deeply-incised leaves, and female trees flower 2-3 weeks later than male trees. Female trees tend to have almost horizontal branches. These methods of identification are not very reliable. Trees may be grown in pots, where their growth will be stunted. Ginkgo will die back if pruned. The tree is resistant to viruses, fungi, insects, pollution and even radiation. Individual trees may live for more than 1000 years. They are very slow-growing.

Sorry, I can't help with sources, though you could try All Rare Herbs in Qld.