Optocouplers seem to be a hot item to manufacture one minute and not the next.
The beloved VACTROL, specifically the VTL5C1 in use since 1997 in what is now the XQP 531A Optical De-esser, has gone extinct - at least from the official manufacturer. The VACTROL is the heart of not only the 531A but also the 545 Optical Disrupter.
There are clones out there, and we will soon be experimenting with some to find a replacement. Hopefully there will be a bright future for the 531A, and 545, and all the products on the market that use these optocouplers.