Hi James, unfortunatley there are no firms doing an upgraded intercooler that I know of for 159/Brera 2.4
Someone like Radtec would happily make a bigger core replacement unit for you, but they would want the car to measure and mockup on and I think you would need to be sitting down for the bill!
The Rs500 intercooler I fitted is a very involved install, that said - Clogz is following my pics very well and we talk indepth about any bits he needs clarity on.
If you feel you have a good basic knowledge of whats under your bonnet and have a decent tool kit and access to someone who can weld up ally for you, then I'd be happy to talk you through any details or I could make up a kit for you.
Alternatively, there is a patent part intercooler on ebay.