IF SOLD OUT, THESE WORK JUST AS WELL, IF NOT BETTER! 

https://surplusdish.com/collections/installation-supplies/products/secure-set-commercial-grade-foam

Q-Set 250-750 is a hydrophobic two-part polyurethane Composite Backfill that expands to fill the peripheral void between a post and the hole. It forms low-density, high-strength composite that can structurally support the post and maintain its upright positioning. It expands immediately after mixing and reaches 50% of full strength in approximately 3 minutes and is fully cured in approximately 2 hours.