All but one of the Spice Girls got together at Ginger Spice's baby's Christening according to
The Sun. The last time the Spice Girls got together was in 2004 when Posh Spice Christened two of her boys. So looks like if you want to get them together you need to have one them hold a Christening. The next Christening should be Baby Spice's who is currently pregnant with her first child.
Scary Spice was not there because she is still in Los Angeles with her newborn baby.
UPDATE: Here is a picture of them all together from Daily Mail:
