Where can I get a Thunderbolt hub or splitter?
I think that this question has already been asked:
Does Thunderbolt support chaining multiple monitors to a MacBook Pro?
To sum it up, it is too early for a splitter or hub for a Thunderbolt port. But you can daisy chain.
And this sums it up as well: http://www.the-cable-store.com/contents/en-us/d44_lightpeak_hubs.html
This is a bit of a loaded question. Though your title refers to Thunderbolt the question solely references display daisychaining, so that's the aspect I'll try to address.
Hardware wise:
Thunderbolt 1 Apple devices have the ability to daisy chain Thunderbolt Displays but it seems that this is an Apple derived solution as TB 1 uses the DisplayPort 1.1 spec which DOES NOT have daisy chain capabilities. So if you have a TB 1 device it seems you are limited to daisychaining via TB ONLY through Apple Thunderbolt displays.
Thunderbolt 2, however, uses the DP 1.2 spec which DOES provide for MST (Multi Stream Transport). Using MST you should in theory be able to daisy chain upto 3 monitors off a single DP 1.2 connection*.
*I haven't found a clear limit on the display max, however given the max data throughput of 17.28 Gbit/s of DP 1.2 we can figure that it would be able to just barely handle 3x 2560x1600 displays at 24 bpp and 60 Hz.
This item here seems to be able to do just exactly that (and similar adapters seem to be found with a quick search):
http://www.startech.com/AV/Displayport-Converters/Mini-DisplayPort-Triple-Head-DisplayPort-Multi-Monitor-MST-Hub~MSTMDP123DP
Software wise:
Prior to the launch of the new Mac Pro there was no MST support in OS X. It was introduced with the launch of the Mac Pro to enable 4k (via MST) by identifying a 4k panel to the computer as 2 2160x1920 panels, whose streams were sent over the wire, identified and pieced together by the monitor.
As of 10.9.4 it seems that MST still does not work in a daisychain scenario in OS X. As far back as November 2013 it was reported working in Windows but I have not seen any information indicating a change in OS X.
Its unfortunate but seems that at this point software is still preventing the proper operation of MST, possibly due to Apple's vested interest in their own daisychaining solution vs DP 1.2.
There is no hub or splitter available at present.
At the risk of leading to further open-ended discussion (something they don't like here on Ask Different), let me mention that Intel held a technology demonstration in September, last month, at their Intel Developers Forum, where they showed prototypes of many Thunderbolt peripherals and devices from several different manufacturers. For each one of them, they indicated that the product would be available for sale sometime in the summer of 2012.
In other words, there will be many types of Thunderbolt devices and peripherals at some point in the future, but there is very little on the market right now.
At the very least, you can get one Thunderbolt display and daisy-chain one of your 24" monitors off of that. I don't know about splitters; I haven't seen any.