If it was sung in the barn at Whittlebury you could try asking Bob & Barbara Brown if they can let you have the recording. Although they only produce 2 tapes from each year's weekend they record, catalogue and archive the entire weekends singing in the barn. If it was in one of the impromptu bits in the food sheds although they don't normally record that stuff it may still be worth asking as they tend to remember who sings what and have contact addresses for most people that attended.