You actually have several options, but none of them are cheap.
The shure thing is individual throddle body setup (they use the cannon manifold and look like tripple webers with fuel injectors on top (Look up itg), but it may require a new fuel injection system (ie electromotive)
horsepower and response possibilities are HUGE but what is your goal here??
How fast do you want to go.......means how much do you want to spend!! As always!!
Regardless, unless you know A LOT about flow theory and fluid dynamics, making your own plentum is a MAJOR undertaking
Az Z car use to sell one, don't know if they still do though. If you're mostly stock looking for a little more power this is an expensive route. I belive they were in the $900 range. I have a home brew one on mine. Cut the factory mounting flanges off about 2" up and hogged the runners out and every thing else is out of aluminum tube. It easily out flows the stocker but the plenum is still a little small. I will someday change that. If you're serious look at the AZZcar one, I wouldn't stick it on anything but a serious motor, turbo or N/A though.
Hey, lots of answers huh? Just want to add my 02 to the mention of T4240Z about ArizonaZ's intake manifolds. Yes these are expensive and no ArizonaZ does NOT sell 'em anymore. However, you may find one at www.Zhome or even HybridZ.org. Myself I have 3 of 'em but currently have no desire to sell. These manifolds are oriented toward performance and will not pass emissions should your state have emissions laws but, of course, he,he, there are several ways around such little problems. Goodluck in your search. shane-