Semisynthetic vanillin is made in ton quantities from lignin from forestry waste. I don't know if they have a "greener" route to l-dopa by using highly enantiospecific "bugs" that have been bioengineered to produce l-dopa, but the big breakthrough that professor Knowles recieved the Nobel Prize in Chemistry in 2001, was for the Monsanto process which starts using synthetic Vanillin. The "asymmetric hydrogenation process" came about by using "chiral ligands" on the hydrogenation metal catalyst, which allowed the reduction of an achiral compound made from vanillin to give almost exclusively "l" dopa with no "d" dopa in it. This was revolutionary, but improvements in yield, purity, and the production giving less toxic waste, are occurring all the time.
Could be that something went wrong when a large batch was made and they had to start all over. But I wouldn't worry about sinemet shortages, it's an easy small molecule to make in ton quantities from cheap starting materials