Mame-bonsai is growing in popularity like shohin at this time. The prize of the larger trees are going lower and lower, because shohin is growing so much still. A few places are keen to develop mame-bonsai (Mame Bonsai or bean-size bonsai is less than 10 centimetres / 4 inches in height. Also the with must not extend 10 cm / 4 inches but there are no official measures).
At a nursery in Angyo, Japan, they specialised in growing mame-bonsai. Many small seedlings and cuttings was produced here. It is quite easy to do this your self. Buy a small raw stock at a nursery and gently cut it back, and let new growth take over, if you do not start with seedlings or cuttings. Specimens with small leaves are required, and then a simple styling and good care to keep the trees healthy. Placing these small trees slightly raises above a tray with water will help keeping humidity higher in the warm season, and the trees healthier.