Contact NEI to see if they make a hollow base bullet for the .41 caliber handguns. That would be as close to a .41 minie as you may get. They also do custom mold making, for a price, or they did. YOu can talk to them about that. There is another man, whose name has been mentioned here several times in the past year, who makes custom molds. Check the links section here, and see if he's listed in the links. I am thinking he is from Colorado, but I could be wrong.
The .41 is an orphan cartridge and caliber. Most consider the PRB too light for shooting big game with about half the states permitting it, and the other half not. The current 40 cal. craze is nothing more than the old .38-40 cartridge in a small, straight walled case, called the 40 S&W. They used the same bullet, and fire at the same velocity- 950 fps. The .41 magnum has never gotten the respect from the public it deserves. Its actually a better long range caliber than the .44 mag! out of both handguns and carbines. Most 41 caliber rifles are given a fast enough Rate of twist that they can handle conicals fairly well, in addition to round ball loads. My brother is shooting a .42 cal. rifle and with 65 grains of FFFg powder, he is getting 1975-1980 fps. and very small groups at 50 yds. Obviously, you are not going to shoot a conical at those speeds, but a minie ball in that caliber would be a very fine deer load, and would take elk, too, out past 100 yds.