Colossus issues

[Fishfan]

My colossus has a broken spring (there is only one spring other than in the pull valve, its not the pull valve that's broken). Anyways, I am wondering what size spring I need to replace it. Is it something I can get at Lowe's? I need to know soon, so I can replace it in time for a water fight the Sunday after New Year's. I have pics, but I can't find where the download cord is, so you'll have to wait for the pics.