Is Portal Games preorder the ONLY way to get the promos? I thought if I preordered it from any site you'd get them? I am pretty sure it is Portal specific. On the website it is only mentioned in conjunction with free shipping and gencon pick-up which are clearly Portal specific. They may be available via other methods in the future, but right now the only guaranteed method is to get it from the company.
As for the OP, the pre-order page (the one that worked) said until July 31st or until they sell out. However, that page no longer seems to work so it may be too late. I suggest subscribing to this thread as that seems to be where most of the discussion is happening.