There is a Thread on it in Here. Just search Shredders concave Spacer and it has a link.
Only lube your magazines when they arent feeding properly, because it renders your hop-up useless for about a full magazine of BB's. No point if its feeding fine.
Make sure its 100% silicon, get the lightest weight you can, you can try RC Car shock oil
and only use 2-3 drops. A little goes a far way.