Either put it back in the hard case, or find the right size shrink. Since you're looking for shrink, I guess the hard case is broken or messed up in some way?

I use that fiber reinforced pkg strapping tape to wrap the cells and keep them from moving relative to each other, but them I shrink on top of that.

Have you looked at the shrink available from Cheapbatteries.com and Maxamps? They should have what you need. If not let us know.