I meant to say try the NCCPG national collections as well.
The two corylus ones are

Corylus Tree Hampshire Sir Harold Hillier Gardens
Corylus (Cobnuts/Filberts) Fruit Kent University Of Reading & Fast Ltd.


I'm sure they'd point you in the right direction.
--
Janet Tweedy
Dalmatian Telegraph
http://www.lancedal.demon.co.uk