I'll make any weight you ask for.
If you must have the mold to fit the Magma caster, I will cut customer supplied blocks for the same price as I charge for my aluminum molds.
That's awful expensive, and especially in such small bullets, I believe you'd be far happier with an LBT mold, which will cast higher quality than iron blocks and at far higher casting rate. If high production is really important, my 4 cavity molds will produce 800 bullets per hour quite easily and be lower cost than having me cut your Magma blocks.