You usually can't grow bloodgood from seed, because they have to be grafted. There's a nice large red maple called acer nigrum that you can get seed for and doesn't require grafting.
If you're interested in growing your own seed then you can try this place
http://www.sheffields.com/catalog/search.lasso?-Token.Z=12645428185
enter acer palmatum (that's plain JM and it will probably show you all kinds of acers.)
If that link doesn't work for you then just look up sheffields seed company

Thanks for the Sheffields link! Looks like a great resource.

Here's another:

FW Schumacher, treeshrubseeds.com.

'Nigrum' Japanese maple is also a grafted cultivar. Seedlings of such named selections may resemble the parent but will not be entitled to its name.

Thanks for the info. I had no idea nigrum was grafted, I just thought it was a black maple. I'm sorry for the wrong info. I'll check out that link.

I have 'Bloodgood' Japanese maples that are asexually propagated.