Have you tried contacting Lee? They build custom molds also, you just gotta get in touch with them and tell them what you're looking for.
From their website:
We make Custom Bullet Molds to your specifications for a setup and tooling fee plus the cost of the mold. When we receive your mold design (submit design here), we will enter in the order and charge you. Our engineer then creates a print and sends it to you for approval. After your approval, your mold will be scheduled for production.
It is our policy that for ALL custom orders you submit payment with your order. If you cancel your order after it has been placed and processed, the charge for the mold is refundable, but the tooling fee is NON-refundable.
Double cavity molds & six cavity molds require a minimum of 2 pcs. to be ordered
Maximum bullet mold dimensions for standard mold blocks (all dimensions in inches): double cavity, .600 dia. .900 length; six cavity, .520 dia. 1.000 length.
Round Ball molds require the use of a carbide ball to create it. These items are expensive, and is reflected in the prices for Custom Round Ball molds. Round Ball mold diameters of .690 and below require a setup fee in addition to the regular mold price. Maximum allowable diameter for custom Round Ball molds is .690. We do not have a mold block to support any larger diameters.
Lead time for six cavity custom bullet molds is 3 months, and double cavity molds is 6 weeks after your approval of the prints we send to you.
Please be aware that any other products ordered at the same time as a Custom item(s) will not be shipped until the item(s) is complete.
Lee Precision, Inc.
4275 Highway "U"
Hartford, WI 53027
Lee Precision Custom Bullet Molds Policy
Our mold tolerance is stated diameter +.003 / -.000 inch. For example, if the diameter dimension on the bullet mold drawing is .429 inch, actual mold cavity diameter can vary from .429 to .432 inch.
We do not guarantee that a custom bullet mold will cast to a specific diameter or weight. If a specific diameter is required it is best to dimension the mold to cast slightly larger, then size the bullet down to the desired diameter. Bullet weight depends on the alloy used in casting. We can provide the volume of the bullet in cubic inches or cubic centimeters, but it is up to the bullet designer to calculate the weight based on the density of his or her alloy.
Custom molds must be inspected and returned if found defective within 30 days of receipt
We do not keep spares for all the different custom mold designs we make. Therefore, if the mold block is damaged by the customer, it will not be replaced. We can still repair damage to the sprue plate or mold handle.
If you cancel your order after the final print has been approved, the charge for the mold is refundable, but the setup and tooling fee is NON-refundable.