There is a Supercharger available for the V6 3.0 ltr: 03-09 V6 Mazda 6 Magnuson MP90 Supercharged Kit NPG Racing
This kit makes up to 450 HP. Your transmission will not be able to handle this (pulley upgrade 12 psi). The pulley upgrade to 5-7 psi is rated @ 375 HP. The 6 speed automatic Aisin Warner tranny is rated to 325 ft lbs torque. Expect some tranny upgrades like: TransGo | AW-TF81SC,*AWF21: SK AWF21 for the 6 speed Aisin Warner. This is a valve body kit that takes 7 hours to install (RE & RE valve body is 5.5 hours). Maybe something else should be done as well, talk to your local tranny shop. An external tranny cooler is mandatory as well as synthetic fluid.
With the standard transmission an upgrade clutch is obvious.
To add to the $4,300 price is a taller hood, larger injectors, pulley upgrade, tranny cooler, oil cooler (all available from same site). This thing needs to be properly tuned, you can't just bolt it on (more $$$$$$). Please inquire about tuning before buying. I also feel a better spark may be required, from upgraded coils. An optimized throttle body or 3.7 ltr throttle body should be considered from Cordova.
Some other obvious upgrades are all new motor mounts from AWR: All Parts - Engine Mounts - Mazda6 - AWR Racing Store .
Buy your programmer here from "The Great NY" who put a twin turbo in his Mazda 6 3.0 litre: http://www.twisted-visionz.com/Online-Store.html
Also, to do this on a stock exhaust is a waste of time. Not sure how pre-cats would handle this. Headers and larger diameter exhaust is needed. Although, if you get the lowest scale model with no upgrades, it might work. I guess the question you have to ask is do you have to pass an emissions test. I would estimate this @ $10,000+ properly done.
I just want you to be aware of the reality & consequences. There are many things that most people don't realize with type of set-up. I have hit on most of the major ones, i'm sure there is more! What do you tell your insurance company?

 

Just tried the link, and it no longer exists. Company probably went under. I heard they made like 20 kits with limited sales.
You may be able to find a turbo kit on-line somewhere or leftover supercharger from original Nautilus, Magnusson one.