You can still rent old Luxtrol units like this one (although probably "newer", from the 50s or 60s) from a lot of entertainment/stage lighting companies. We have two of them in the booth on our mainstage at Portland State.
I've also seen a few that allow you to adjust the output voltage, up to 150 volts or so. They are commonly used on followspots to give the spot an extra "kick", even though it results in significantly decreased lamp life.
I always understood that they were only to be used with the control knob in the "up" positon.
