I thought I remembered the unior tool being hard to find a while back. If I was remembering that correctly that seems to no longer be the case. A google search for "unior cassette lockring tool" will bring up a bunch of sources. A video search for the same will show how it works. It weighs less than an once, can be found for under $10, and doesn't require any chain whips. It also doubles as a spoke wrench.