Unfortunately the collets in Bosch routers are proprierary items and are unique to Bosch as far as I am aware. They look similar to the deWalt DW625 ones but the seating angles are apparently different, so you are probably stuck with buying from Bosch.
Strangely, they have a collet listed for all Bosch routers exept the GOF2000CE, but thanks for the info Chas, much appreciated. It seems i'll have to order one from Bosch via my local suppliers.
cheers,
jonathan.