Pokemon Platinum HELP! 3 regis.?

Well it sounds to me like you have a slight misunderstanding. The only Regigigas that can work in this case is the one that was distributed at Toysrus from March 8 through 21. The only thing that you could do if you didn't get one is either trade someone who did or cross your fingers and hope they have another event. Also, just a heads up, there's going to be a Nintendo event starting April 20 running through May 12. This time it's to get the Key Item, the Secret Key which allows you to open a door on the first floor of the Eterna City Team Galactic building. It allows you to gain access to a room with five household appliances which have the ability to change Rotom's form. Hope my help...well, helped you I guess.