Spare BA simulator capacity can be bought through Virtual Aviation.
Have a look at
www.virtualaviation.co.uk.
I have used them to buy A320 sim time in the past - not for fun though (but it was!). However BA sims are expensive.
European at Bournemouth have an ex-BA 747 Classic that may be available. Again I have used European's 727 and TriStar sims.