That's the only way to get a 6IV Ditto without cheating since you can't breed them.
If you have a friend safari with a Ditto, you are guaranteed 2 perfect IVs, other than that you have to be lucky.
You could chain them to increase your chances as well, but that would take a bit of skill in chaining too.
[Here] is a guide on chaining.
And as fondant commented, this has a high chance of breaking before getting to 61, so I wouldn't rely on it.