You could ask Mr P the brand he uses. Might make it easier to find a supplier. His email addy is on his website.
If you're talking about the bit in his DVD where he is sitting on a drum stool, I thought that was a cymbal stand. (I could be mistaken - I accidentally rendered my copy unplayable.)
The alternative to a short stand is a tall seat. I alternate between standing and sitting on a bar stool - no adjustment of the theremin stand required.