I'm guess by the lack of responses that there is no such thing. So how about a source for suitable .30 cal frangible bullets so that I can load the rounds up myself?
If it helps, the reason that I ask is that I am an LEO and I'm looking into options for extremely quiet removal of cameras and other material. Or as I would tell my boss "discreet anti material" ammunition for use during high risk warrants and hostage rescue missions. I've asked around in the usual law enforcement circles and come up with nothing for .308's. I have frangible for my mp5sd but that it is very limited in terms of distance and accuracy.