You don't need to buy anything! Everything you need to run Alpha is available to download for free after you create an Alpha (leaders) are added as a team member.
If you really prefer a hardcopy DVD or books, here are some resources that you can purchase through Amazon.ca, Parasource or your local Christian bookstore.
Alpha Film Series DVD | Approx $60.00 Cdn
Alpha Team Guide | Approx $12.00 Cdn
Alpha Guest Guide | Approx $12.00 Cdn
Alpha Youth Series Discussion Guide | Approx $12.00 Cdn