You're able to use /head [player name/custom head value] to get player heads. If you want a discord one, you can use this command:
/head eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvNGQ0MjMzN2JlMGJkY2EyMTI4MDk3ZjFjNWJiMTEwOWU1YzYzM2MxNzkyNmFmNWZiNmZjMjAwMDAwMTFhZWI1MyJ9fX0=