The 'Quantity' button on the Amazon product page will appear to suggest a maximum of 30, but this is not the case. The option to purchase larger volumes is given later on in the ordering process. The guide below explains how. 

STEP 1: On the Amazon Product Page leave the quantity as 1 and select 'Add to Basket'

STEP 2: Select 'Proceed to checkout'

STEP 3: In 'Review items and delivery' change the Qty to 10+

STEP 4: Enter the number of copies you would like and then click "Update" (which will appear just beneath it).
             Click 'Buy now'