From their announcement:
Darkson Designs is pleased to announce that their new webstore is open for business. Currently they are offering free shipping on printed rulebooks within the continental US.
Furthermore, Darkson will be adding the rest of their product line to the store within the next few weeks.
In the meantime, you can order any of their product line from your local game store, or the AE: WWII core rulebook in PDF at Wargame Vault. They are currently only accepting payment through PayPal.