Strange as it may seem, and I know they are not 'popular' as a freight company, but you should try MK Airlines at Landhurst, near Gatwick. They have fairly recently received a UK AoC, but not for their DC8s which are all in Africa. The DC8 sim was housed at their Landhurst HQ and they MAY have one/some of their UK licensed instructors 'ticked up' on it. Try it, if they can't help then they may be able to give you a steer in the right direction.
www.mkairlines.com