How badly do you want to shoot .357? You might be able to get an .38 caliber M&P cylinder and barrel easier than the .357 cylinder.
I thought that I had been to the mountain and saw the elephant, but a bulged cylinder? I really didn't even think that was possible, that the cylinder would crack before it bulged. If you have a bulged cylinder, then apparently I was in error. Maybe you should get a second opinion, JMHO