The Trustee, The Bank of New York Mellon, does not deal directly with the public. The Trustee handles creation and redemption orders for the Trust’s shares with Authorized Participants, who deal in blocks of 100,000 SPDR® Gold Shares. An individual investor wishing to exchange shares for physical gold would have to come to the appropriate arrangements with his or her broker and an Authorized Participant.
http://www.spdrgoldshares.com/usa/faqs/#q4fa24b4ed60b5
Note: 100,000 shares is $125 million at $1250/oz.