From what I hear, cat-style butt plug tails are rarer than hen's teeth. Your best bet for a pre-made one would probably be a rather long fox tail.
There's other ones there:
link
They're rubber plugs, though. Not as sanitary as the glass one Liberator carries.
In both cases, they're real fur. The one from Liberator looks like it's interchangeable, the other is attached directly to the plug.
If you're an artsy craftsy person, you could see about getting a fox tail and a silicone plug you like, and attaching one to the other. The advantage is you get to choose the plug, and the tail. If you go for real, you can get as long a tail as nature offers (and just a tail won't break the bank, either). Or, you could buy/make a more cat-like tail and attach it to the plug. Total cost would end up being much lower than retail (a decent, simple tanned fox tail can be had for <$15; add the price of your plug of choice), and you'd get a lot more customization.