1969 20' 40gal fuel tank under console ques.

[69Seacraft20]

Hi I'm new here. I recently bought a 69' 20 footer w/200 Mercury Opti. After doing some research I realized this boat doesn't have a below deck fuel tank and originally there should be a tank under the forward console seat, there is not. Previous owners used portable tanks for just near shore running.
Does any one know where I can find a tank that will fit in fwd console?

Thanks