Where to get stabilitron voltage current characteristics
There is a zener voltage and a zener test current, which tell you the expected performance point around which the plot will be drawn.

Then there is the zener current maximum, which lets you know how far the plot could go.

Then it's likely the plot will look similar to that of others, when you adjust it to orders of magnitude from the test current, but that's not a guarantee, just an estimating tool.

For the operation around the given set point of Vz and Izt you also get (in most cases) the Z(zt), which is its effective resistive response around the operation point. Which means that for small changes (less than half an order of magnitude-ish) you can use that to estimate the voltage change.

i.e. for the 1N4099, you see it typically is 6.8V at 250&mu;A, but has a 200 Ohm Z(zt). So if you'd increase to 500&mu;A, you could expect it to go up by about 50mV (there's always small side effects), per: V = I * R, where I is the current increase and V is the voltage increase caused by it.

To emphasize again, if you go from 250&mu;A to 25mA this will not work, as other important non-linear factors are involved.

If all that combined is not enough detail to work with, the only two ways are to:  


Google "IV plot" + device name.  
Measure it yourself.


Being aware that testing 1 or 2 gives no real data for the general type or even your specific batch, all devices will be within a tolerance, but the distribution can only be gotten from many devices (least 50, preferably 5000).

All that said, if you look at the range of voltages at its specified point, 6.46V to 7.14V it is unlikely you will need a very accurate plot, because the uncertainty in its base value is pretty high. Of course, that's untested. If you test them you'l be much more sure of their reverse voltage, because they are much more repeatable than accurate.
The point is, for a datasheet, which describes a whole range, it's not much use giving you a very accurate tool for estimation, if it can be off by a roomy 10% or more.