I have been in touch with the VERY helpful Daniel Sable at CILIP HQ who has checked the details and has confirmed that if you do not know a named contact at the AGM on October 15th you can send your proxy voting form to Ridgmount Street naming the "Chair of the meeting" as your proxy, and stating the address of your proxy as 7 Ridgmount Street, (the full address is CILIP, 7 Ridgmount Street, London WC1E 7AE - and this is also where you need to post your form to.)
The text of Daniel's email is quoted below for clarity:
As you know, the Regulations prescribe every individual member who is entitled to be present and to vote at the AGM has a right to have any votes tendered accepted at the meeting. In this regard, members casting their votes who do not know a named person in attendance at the AGM should appoint ‘the Chair of the meeting’ c/o 7 Ridgmount St as their default proxy. By doing so they ensure their nominated proxy is present the meeting.The full subscriptions proposal is available for all to consider in advance of casting their vote, and there has been lively online debate over the issue which is well worth a read, (Twitter is currently full of examples, or go to the entry on Gaz Johnson's blog for a good variety of suggestions and arguements in various directions, and see Tom Roper's blog for interesting points as well).
It is well worth getting involved and having your say - and seeing what others think - member engagement and debate is really important and the period leading up to an AGM is a great time to get involved with it.