At present your website is lacking relevant industry content. May I suggest you create a company page for each exhibitor (currently you just have logos with website links) to provide relevant news editorial regarding their products and the exhibition. This may contain links to specific pages on the exhibitors website. This can be updated during the year. Ideally this would be self service.
This would improve your rankings, provide a platform for visitors to plan their visit, they would spend longer on your website. You become more relevant.