There is one explicitly listed on the coreboot mailing list a few times. On the other hand, there aren't a whole lot of up-to-date coreboot setups for Intel anymore. For recent AMD platforms, there is none.

If you really want to use coreboot, your best bet is to first look up what platforms are supported (i.e. 6th generation Intel) and then look for an ODM that is making a 6th gen system. Next step is to simply ask if they fuse BootGuard or not, and if they do fuse it, how much of it. In many cases you can't run Coreboot in pure form anyway, some blobs will remain to get basic functionality working. If you want a deblobbed boot your options are practically restricted to very old platforms, or 2 or 3 commercial offerings.