You really can't find a kit as it's more complicated than adding just a turbo. You need to find a turbo car and swap all the different parts to the Rampage. This would include fuel system, exhaust and cooling upgrades, transplanting the motor and transmission from the turbo car and then rewiring it all.
Here's a good overview: http://www.thedodgegarage.com/ddg_faq.html
There's a lot of differences between the carbed 2.2 in the Rampage and the fuel injected turbo 2.2. It can be a fun project, it just isn't easy.
Theoretically, the 2.4 turbo from a PT Cruiser or an SRT-4 might work too. Its the electronic giblets that would be the tough part. I hear tell if you start with a 2.2/2.5 block, that the heads from the 2.4 are a relatively straight forward swap. That gets you a 16 V, crossflow, DOHC head that should be pretty comparable to the Lotus-designed head from the Turbo III. Even better is if you get the turbo 2.4 head since its supposedly a little beefier, and it has those added oil-squirters that keep everything lubed up good.
Either way, hats off to you if you pull this off! The Rampage is a VERY cool little rig and it seems a natural candidate for a worked up turbo plant!