I know that Parc Aviation do some cabin crew recrutment. Or try IAP Avitation Services
IAP Technical Services Ltd
The Maltings, Southmill Rd
Bishops Stortford, Herts
CM23 3DH
Tel:- 01279 508 777 or visit their web page:
www.iapgroup.co.uk/ts
There are also quite a few agencies in the back of the Flight International Mag.
Good Luck