Well, same problem as I (and most other shops also, I guess) do have:
They only ship about once a month. And you need to preorder for the next month.
Same with my shop: I have 50 or so in stock for 1 or 2 weeks, then I have to wait three weeks for the next batch.
And I can't restock more than 50 at once, because I simply don't have the money...