Probably a Lyman mold for the Great Plains bullet would be about your best choice for a .50 conical that might shoot well. Bull Shop makes a number of .50 conicals mostly intended for White Rifles but could be sized to fit the bore of your Omega (probably .500 or .501). Perhaps getting a few of his in a two or three different types would be a good test to see if the rifle will shoot any of them well. You could also buy some Great Plains conicals and try those before shelling out for a mold. About any other mold you get for the .50 in a full-bore would have to be custom made. There are some older Lyman molds that might put out a workable bullet if sized, but you would have to watch the classifieds sections of various forums to ever find one. Rapine also made/makes a mold that drops a .504 bullet that could be sized down to fit your bore, again those are pretty hard to find as well.
In the .429 or .451 sizing to be used with sabots, there are a ton of ready-made molds you might give a whirl. An inexpensive one to get started with would be the Lee 457-340-F sized to .451/.452 then used in a Harvester short black .50/.45 sabot. I would size them with a smear of Crisco or similar then wipe off the excess.
That's about the best advice I can give you