I came across similar questions, but my doubt still remains. Yes, there is a portrait of Dumbledore at Hogwarts, and it was impossible for Harry, Ron and Hermione to access it during DH. But why couldn't they create one themselves for guidance during the Horcrux hunt? I know portraits are just imprints of the person and only reflect the personality of the dead person. But there is no denying that the portrait Dumbledore guided Snape through the year. And that the portrait would have been invaluable to Harry, Ron and Hermione.
Is there any information on how these portraits are created and who creates them? If you need an artist to paint Dumbledore, and then enchant the painting, could they have found a muggle artist who could do it for them and then cast the spell themselves? (While they remained disguised. Dumbledore could have been any old man dressed in funny robes. Any story would have worked or they could have performed a memory modification if it came to that)
Given the amount of struggle the trio goes through to figure out Dumbledore's intentions, they must have thought of this. Especially when they ask Phineas Nigellus if he could bring the portrait Dumbledore along.