Display frequency is not published for security reasons; this has been done for the last 3 shows at least. No-one except ATC/Flying Control Committee/pilots has the need to know anyway.
It's all too easy for someone to buy an ICOM or similar nowadays and unlawfully transmit on any frequency, thus blocking it for essential messages; the Mig 29 collision at Fairford was part attributed to the frequency in use being congested with non-display traffic, hence Farnborough use different frequencies for display and tower.