If you want clean dead dry rock AP usually gets nice pieces in. You can check often on lfs fb pages when live rock gets shipped.
Or you can go the craiglist way. Theres a guy i met one day at a lfs. He was drunk and i had acouple drinks before going there but this guy was toasty. He gave me his number has big large pieces of rock. Back story seems this guy has like 15 systems running...he showed me his systems fotos and from one 300 tank he probably had like 500lbs of rock in there. Pulled it out to rescape and still has large pieces.
I can send you his txt if you wana talk to him.
Said something like 2bucks a lb.