thatīs a good question.
Since I planned to leave the Tanks off of my kit, I wasnīt looking for any replacements. The only Set Iīm aware of is the Royal Model Set which has replacement tanks. I donīt know in how far those are correct and if they include the fittings for them.
Maybe someone else knows more?
From some of the pics Iīve seen, it shouldnīt be too hard to scratch some of the fittings.
I really like this Walkaround and it gives a nice view on the area where the tanks are supposed to sit: