This season's Powergen Cup final between Gloucester and Northampton Saints is expected to attract a sell-out crowd at Twickenham.
There are around 1,500 more tickets available through Ticketmaster for Saturday's big game (4.30pm).
The Powergen Cup final is the climax of a day of rugby that starts with the Powergen Junior Vase final between Shipston-on-Stour and Old Alleynians (10.15am)
St Mary's take on Hertford in the Powergen Intermediate Cup (12.15pm) before National League One rivals Orrell and Exeter meet in the Powergen Shield (2pm).
The remaining tickets are priced from £24 to £30. To book call Ticketmaster on 0870 9020000 or go to www.ticketmaster.co.uk