Looks like I need a new radiator for a JDM Foz STI 2006 facelift model, are there any uprated alloy ones available? 

for road use it no real benefit .

mishimoto is option or nissens for a direct replacement . I believe oem p/n on yours will be 45119SA020 but I not in the shop to check on that 100% .

120 to 350 is rough price range from nissens to oem and mishimoto 230ish . if do fit mishimoto think twice before using increased pressure rad cap, absolute no need increase pressure above factory spec for road use in UK climate and with engines known factory HG issues it not a wise move .

Probably should have mentioned that I need to replace a failed radiator not doing it just for the sake of it! I had contacted Mishimoto but they said they didn’t do a radiator that fits the Forester STI? 

In relation to the pressure cap the one that came with my car is the standard 1.37bar cap so I was just planning on reusing that one?

Mishimoto do one they just don't now it fits the sti .

Just use the oem subaru part number to see model variants that use that rad, oem cap is the best one to use imo .

Excellent thank you for the advice!