Vintage Speed probably has it, check out their main page: www.vintagespeed.com This is their mainfold page http://www.vintagespeed.com/Manifolds.htm I remember seeing an intake for a 331 somewhere on that site..might have been desoto
Weiand made a nice 3x2, they pop up on ebay from time to time- you can put in a automatic search to help keep tabs on it. Be prepared to pay though- the last blasted intake went for over a grand... I seen a dirty one with no carbs sell for eight hundred.
I have a WC3D for sale that's drilled from the factory for 4 stud carbs. Oh and that's the remains of a paper gasket sticking to the front carb pad not corrosion. Tom