Brian Collingwood's site is the most informative that I know of on growing clematis from seed. This link will get you to it: Clematis from seed.

Hi Kms, koreana is quite easy and the seedlings are beautiful and quick-growing. There is no specific data on my site since I've not got around to posting the pre-1988 data (about 50 koreanas raised) yet but if you need any help drop me an email. use the standard method (as per site) and things will go fine.