Try your wrecking yards. Remember that the new used individual rockers on a unit should be installed in the positions they were operating on with the used cam. So you want the used cam and it;'s rockers plus them numbered.

I cannot see having to remove the head to change the cam. Although I have never worked on a m110 engine. If for any reason you cannot locate a cam. I can recommend a place that builds up lobes and regrinds the whole cam. In my experience they do a good job. Make sure the hard wear surface of the rockers has not worn through. When it does it is quite visual it has done so.