I know of the wish spell being a possible solution. Are there any others? I'm asking for a 13th-level non-multiclassed sorcerer to be able to learn and cast simulacrum, as if it were on the sorcerer spell list.
Is there an official way to add simulacrum to a (non-multiclassed) sorcerer's spell list, besides the wish spell?
The DM is allowed to change some (read: all) of the rules as they see fit. On page 287, there is a subsection titled Changing Spell Lists. By simply asking your DM, they may decide that Rule of Cool wins here, and let you select it. You may wish to suggest removing some other spell from their list, but honestly for Sorcerers, this is pretty lame. You'd have had to ignore some of those level 7 spells anyway unlike, say, Clerics.
Wizards are all about arcane research. Ask your DM what it would take for such a researcher to invent a new spell, ritual simulacrum, which behaves exactly as simulacrum but has the ritual tag (see DMG 283, Creating a Spell). From there, your sorcerer would need an int or wis of 13 or higher for the Ritual Caster feat. From there, simply copy it into his ritual book.
Blessings (DMG 227) are supernatural gifts bestowed on a character. Generally, "a typical blessing mimics the properties of a wondrous item". I'm not aware of one that adds spells known like this specifically, but your DM may be willing to consider this an appropriate reward for some task.
