They sell a kit with a new spring, oring, clip, and lubrication, but it doesn't include the housing push button.
I've never seen anyone break one of those, that is very impressive.
I can't find that part for sale. I am pretty certain that the housing push button is the same on all of their DSLR housings, so you could buy a cheap housing and move the part over, but I am very certain it will be cheaper to email Ikelite directly and buy that part from them. They are good people, they have always bent over backwards to help me out with far less serious complaints or issues than this.