Hi,
I need a inductor part that is rated for 1000Volts. Can I use two inductors ( rated for 500V and half the inductance of required value ) in series?
Yes, the voltage drop across each (identical) inductor should be 1/2 the total.
The tolerance of the inductance values will cause that voltage division to proportionally vary, of course.
Once it is not clear the inductor tolerance you are about to use, and considering that you can achieve accurate values with resistors, I would think of adding high value equal resistors in parallel and "center tapped" with both inductors - likewise we often do with electrolitic capacitors in series - just to better ensure proper voltage balancing.