If you do a Google search on "Japanese maple seeds", you'll turn up various sources that sell them. But it will be easier and cheaper to just gather some from existing trees......any neighbors or friends that grow them? You could even purloin a few from an arboretum, botanical garden or larger nursery in your area that carries or grows these trees :-)

Should you do mail order, be aware of those that are attempting to sell named forms of maple seeds. Named forms of J. maples are propagated ONLY by grafting or to a much lesser extent, by cuttings. Seedlings will only be generic J. maples - not named forms - and may vary considerably from the parent plant. But you can grow some very nice, if unnamed, trees by this method.

Here is a link that might be useful: Google search for J. maple seeds

I have been growing Japanese maples from seeds for years. As Gardengal48 says, the seedlings may vary considerably from the parent plant, so pick a good plant for seeds to begin with.
I grow the seedlings in pots for a few years to get them up to size for planting out. In that time I evaluate them for good qualities. Fall color is probably the main characteristic that I look for, but there are other qualities to keep in mind. New growth color, vigor, and the color of the seeds are things to judge them by also. Bright red seeds can look like blossoms from a distance.
I have well over a hundred Japanese maples and only four are named grafts.

Here is a link that might be useful: Fall Maple Album

I planted about 50 seeds in a seed starting flat and only three have grown and survived to about 3". I would like to transplant them to a bigger container, but was wondering the appropriate size for this next step up. This is my first time growing them. I have the generic Japanese Maple. Thanks

botann,

Your maples are GORGEOUS! Now I need to run out in the yard and gather up some seed.

Is there any trick to starting them, like putting them in the refrigerator for a while?

Fall is the time for gathering seeds, not now.
I used to put seeds in flats and leave them in a protected place for the winter and then plant out in raised beds after they sprout in the Spring. Now I just look for volunteers under my best trees. An aged wood chip mulch seems to favor the seeds to sprout on their own.
I have stratified other seeds, but not Japanese Maples.

OhioCC,

Send me a message this Fall, I'lll send you some seeds from trees I grow. Even if you have just a little success it's exciting and you learn alot about germination and patience.

UBC has a good thread about JM seed germination.

Here is a link that might be useful: UBC Japanese Maple Seeds

Thanks for all the good info on when to collect and how to start. I might have to try some this fall!