Assume it's a mess ball Lee so am surprised previous PMC/PEC's haven't already got a contacts folder/file for just these occassions.
I helped organise a couple as PMC and as PEC during my time.
The decoration could surely be done in-house and be a lot cheaper, always some young soldiers looking to make a few extra bob in ED pay.
I created something similar with a Grotto which I used a 9'X9' and decorated with coloured crepe paper and cotton wool and the likes. Found it was appreciated more if the members knew it had been done by their colleagues. Externally done will cost a fair wee bit.
Mind you us Infantry types where never afraid of a wee bit work and being Scots, where tight as hell until it came to using funds for alcohol

Geo