Hey Chris,
Long time no see. Still working in Hayes? You missed a great day out at Billing this year.
Afraid I can't help regarding a source for your radiator, but we had ours replaced when they did our transmission (in hindsight, we should have just added an aftermarket transmission cooler instead).
IIRC The Subaru dealer ripped us off for about 800 quid to supply and fit a new radiator.
This thread may help.
http://www.subaru-svx.net/forum/show...?threadid=1495
Phil.