Tom at Accuratemolds.com does this very quickly. 'Tarawa' and I already have used him with good sucess. Tarawa 's mold is for 12 g and is shown in th catalog. Mine is the 550 and 675 grn .622.

Dual cavity, dual weight mold and he didn't bat an eylash at the thought nor charge more! Most makes would laught at you for even thinking of this idea.

http://www.accuratemolds.com/

(edit) Your choice of materials. Brass, aluminum, or cast iron. Uses Lee 6 hole handles or RCBS IIRC.