Try
www.gbax.com
Update: Just checked and they are no longer stocking Jap PSP's.
Newcastle based and pretty reliable and cheap. Also,
www.gamechoice.com.hk if you want to order from hong kong. I've ordered all kinds of hardware from there and never payed import taxes. I stay away from lik-sang due to charges.
A friend of mine bought a Panasonic q from there and got stung £80 tax..