Did you find a match? The suntour VX stuff was made by Sugino, I'm pretty certain, as sugino did all the suntour cranks. So, you can buy a sugino maxy or super maxy crank arm and it will be more or less a perfect match (except for the writing in the flutes, but made by the same company in the same forge.)
alternately, you can buy any 1970's left arm in the correct length, which is probably 170mm, such as SR/sakae, sugino, campagnolo, gipiemme, stronglight, etc. All of them made a basic fluted crank arm that's functionally equivalent to yours. You can even file/grind out the 'VX' from your crank (I'm assuming it's embossed) and file/grind out the 'Super Maxy' to get an even closer match.
Alternately, there are places like SJS cycles that sell a very good FLAT (not arc'd / not modern) replacement left arm, in the style of the 1970's. Good luck!