AT used to make a shock mount for the 40 series (but I think it works with the 30's as well) that has a locking "nut" on the bottom of the shock mount that has 3 rubber pads that grip the mic and hold it in place. I have two of them and they are very very sturdy. I looked on the AT site and couldn't find it anywhere, same with a google search and ebay. I'll see if I can find a part number on the mount when I get home tonight.
The ones that come with the mics are great and they get the job done well, they are just a pain in the ass to get the mic in and out of the mount. These other mounts, all you had to do is give the bottom a quarter twist and your mic was free.