I have uploaded the blue spiny shell here:
http://www.mediafire.com/?zwuncznminf
Note: The common3.pac I've uploaded is PAL and maybe don't work on NTSC. To get it working open BrawlBox, extract the ModelData[0] and the AnimationData[0] from the directory ItmSmashBallBrres (ARC) and replace it on a NTSC common3.pac.
Tutorial to get the mario kart wii model working on SSBB:
1 - The files of MKWii are in .szs format and you need SZS modifier (created by Chadsoft) to extract the Brres you want (for example: koura_red, togezo_koura, etc)
2 - Once you have the desired Brres, follow the instruction of RandomTBush posted on this thread:
http://www.smashboards.com/showthread.php?t=263127
3 - And the last step is to get the other games Chr0 animations working in BrawlBox. I done this:
a - Download the latest version of Brawl Box (v0.63d) (credit to Kryal for making this awesome program)
b - Click on the Chr0 animation yo want to preview and yo will see four fields: FrameCount, Unknown1, Unknown2, Unknown3. Fill unknown1, 2 and 3 with 0 (although sometimes the field Unknown2 can be filled with 1 when you are working on animated stages for instance) and fill the FrameCount field with a high number (500 for example). Give a name to the animation (rename it as you want) and know go to the model (.mdl0), right click --> preview
c - See when the animation ends. You can look a bone that changes constantly, you can note this because when a animation ends this bone jave almost all his parameters (X, Y, Z translation, etc) in yellow and reduce the FrameCount to the final frame number (in case of Blue Spiny Shell the end is frame 60).
Enjoy
and sorry for my bad english and for my probably bad explanation.
Edit: I had forgotten that the blue spiny shell appear too big in game (10 times bigger than in the screenshots taken by me) and you'll need a code that makes smash ball smaller. Sorry I have tried to resize the main bone to 0.25 but it didn't work :S