Casper - I believe the suggestion is that Lee will cut you a mould in the REAL design, which would result in a typical paradox-weight - for about $100.00 to $125.00 I think is their range for a simple, custom mould.

Foster (American-type) hollow-based 12 bore slugs will run from .690" to .725" - nominally, depending on their maker.

Brenneke's are usually a bit larger in diameter and have been sold by the box of 25 for loading, in the past - what their size is I do not know.