I measured the sink, including the location of the partition. I bought the cutting board from Wal*Mart, knowing it was oversized for the 1 bay.
I made a pattern using cardboard and scissors.
I used a sabre saw to cut the 'top' off to fit the profile of the sink.
I discovered that pushing the saw too fast only melted that plastic and it re-fused behind the blade. (awkward) Re-cut and smoothed/final shaped with sandpaper.
So, the answer to "Bought or Made?" is "Modified a store-bought piece."
I think I created a thread about it sometime after Memorial Day 2015 (or it could have been July 4).