How do you feel about stratification techniques?
Did you try anything to improve germination rate? I collected a lot of stuff from several american sites on this subject, such as:
www.wpsm.net
or
"the seed germination database" available in a lot of on-line seed stores, like
http://www.backyardgardener.com/tm.html
... if you take some time to read, the texts aren't that dense.