Wikipedia informs me that Gloria Baker's Shark — a Porsche 928 that could turn into a submarine — was never released as a toy, even though this was her main vehicle in the TV series. Considering that the toy line came before the TV series and this vehicle was introduced in the second episode, this is quite remarkable.
Do we know why it was never released as a toy?
As mentioned in the comments, toy versions of Shark do exist, but they're unofficial versions made by hobbyists.