Since there have been so many requests, here are some possible solutions for performance additions and exterior modifications. These are the best we've found so far:
Irmscher- I dont know if they will send to the US. Call them or email them.
Part specification is the same as above. On the side bar, go to Accessories Programme > Omega > Till 1999 (97-99) or From 1999 (2000 -) > Saloon only. Catera is 3.0 V6, Lucas Brakes. Dont select estate/caravan.
Again, not sure on their status on shipping to US.
Go to Tuning > V6 Tuning. Most things should theoretically work except for all of the throttle bodies, and the items for the 2.5 V6 unless it also says 3.0 V6 is compatable as well. For example, the power chamber resonator works on both engines.
Http://www.tirerack.com Various brake applications, tire, suspension.
Http://www.knfilterchargers.com/search/appsearch.aspx - Hi-flow replacement airfilter. Part # 33-2734
http://www.drivewire.com/ - Sparkplug wires (97-98), Intrax lowering springs (must disable rear leveling system!) and camber kits.
Http://www.ultrarev.com/ - Magnacore leads, ignition.
(thanks 97 Catera)
(I am not endorsing use of any of these products. I myself have not tested each item for its compatibility so I cannot guarantee that it will work. Aftermarket accessories may void your warranty or alter the operation of the pollution control systems on your vehicle. Use at your own risk!)