HLS2k

If I wanted to upgrade to an aftermarket ECU, where can I get it installed?

AusS2000

I'd work out what ECU or piggy back you want, then get a list of installers in your area and a few references.

4IGS2000

There are many ECUs
The AEM EMS is one of the only stand alone systems available..
Spoon/Mugen/Amuse/Feels are just other japanese tuners that have hacked the ECU to perform well with their products! You can purchase their complete ECUs starting around $1000