You can order on RS-Components or Element14. You will be put on a waiting list.
Due to outrageous demand, quantity is currently limited to one per customer.
I ordered one from Element14 la. It has 256MB and 2G SD support. Class10 is not supported now... They are thinking to add more ram and SD support in Model B+.
Any brother has good relationship with Element14 can help us to get one.