Another resource that i used a lot because they always had what i needed is Simplyspeakers.com
And i think they were the ones that gave me the CD to use for centering. It worked great.
In my experience, I have not liked the outcome of my Re-foam job and pulled the surrounds off to do them again.
I don't see an issue doing it more than once or twice as long as the cone survives.
Good luck on the project!