Depending on what sort of volume you're talking about you *can* take physical delivery (properly known as "load out") from COMEX. The minimum quantity is buried somewhere in the futures contract... I'm assuming it's large-is.

With regards to the assay, I'd say the party providing said assay is as important as the concept of obtaining an assay itself. If I were buying a significant amount of gold to hold long-term I would probably want a third party to do the assessment.

A quick search of "APMEX Complaints" yields enough bad stories that I'd steer clear of them. A somewhat common theme seems to be people plunk down money for bullion, a shipping label is created but the shipment is never given to the processor, a few weeks go by, APMEX says "there was a problem with your shipment" and the buyer is refunded. In five minutes I saw enough of them that it seems systematic and, tbh, I can see the business logic.

Buy a gold ETF.