Dang I just sold a big chunk to someone else the other dya.
As a last resort...you can always do this. This is where I got all my base rock. https://www.amazon.com/Worldwide-Imports-AWW0855-Atlantic-40-Pound/dp/B0002DI7F0/ref=sr_1_3?keywords=base+rock&qid=1547844054&s=Pet+Supplies&sr=1-3