I did use this once with a borrowed arranger keyboard (gem wk8) this keyboard has a PAL output for direct display on videoscreens.
A lot of the higher end arranger keyboards do have this feature these days, but I am not aware of any synth having this possibility.
You might adress your question on the General arranger section of this BBS.
There are a couple of posters there using only software who might be able to help.
Fred
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Keyboards/Sound Units: Kurzweil 2600S, Roland VR-760, Acces Virus C, Roland G-800, Akai AX60, Minimoog, Machine Drum, Roland R8-M, mediastation x-76