Search this forum for ¨grommet¨ somebody asked this the other day. It was for a Antec case if i remeber correctly. The posts list places to buy these things.
You don't need to restrict yourself to Lian-Li kit. I replaced all my X500 hard drive grommets with Antec silicone grommets as I found them better at absorbing vibration and preventing them from being transmitted to the case.