I think you will struggle. Unless you pay 3 or 4 times over the odds on ebay. They are sought after and rarely get sold unless by money grabbing touts i'm afraid.
New to Piston Heads but I have a spare ticket for Houx Annex. I purchased 4 from tickets2u but due to a few people dropping out we have a spare. The tickets are due to be posted out this week according to tickets2u. If you are interested please reply or drop me a message.