I am in South Africa - basically same climate as the Australian East coast - specifically - on the garden route George Western cape. Lilian

In the U K I would go to Chiltern Seeds, they have a wide range of tree seeds ( well most seeds)
check out their website by googling chilternseeds.co.uk
And ask for advice

A word of warning though - Acer palmatum varieties are usually grafted onto a stronger rootstock than their own, so if you grow from seed, the plant will be using its own roots, which are weak growing.