I generally make a silicone mold from an original 78 but will occasionally cut one on my c.1940 Presto 6N and then make a mold of it. Silicone is expensive, recording blanks were expensive and are now non-existent (since the Apollo fire). Cutting sapphires are expensive and it cost thousands to get my lathe in good working order. People ask frequently but unfortunately only one person has ever been willing to pay for a custom 78.
With over 400 sides in my catalog, ranging from "desirable" to "rare as hens teeth", you'd think that I'd be able to make some money but that's never happened either. Now consider that most of my discs are $20 - $40 each, which is the approximate range of what a new vinyl disc costs. Who the heck is going to spend hundreds of thousands of dollars to sell a few hundred copies per year?
There are two people in the world selling shellac-compatible 78's, Vulcan is the other, last I checked he had 4 titles available. I've even been encouraging others to start making them and have been teaching anyone who cares, that has resulted in one more person (gradually) entering the market. It's a lot of work and no money, but if that sounds like a job you're interested in, just send me a message