I'll just have to keep looking..
I used to have a Browning Hi-Power in .40 S&W and I fitted a Fire Dragon ported .357 SIG barrels to it. Very accurate and quite manageable but I got goofy and sold it to buy something else.
First lesson in life: if you have something that fits and shoots well, Don't Sell It!
I was thinking the exact thing for a personal defense pistol, using a .40 High Power and having .357 Sig barrels made for it.
I shot a friends Sig 229 with the drop in .357 Sig barrel, and I was impressed.
I have also thought about using a .45 ACP pistol for a .400 Cor-bon weapon, but they are still making the good old 10mm.