WattStop was bought out by a British company named Firing Circuits who made battery chargers and effectively shut down as a soft starter manufacturer a long time ago (10+ years). Firing Circuits was eventually bought by a German company named Digatron, who does hybrid vehicle power systems but still has an office in Connecticut. You might contact them and see if they retained any WattStop records, but it's not likely.
It was never a very good soft starter though, might not be worth salvaging.