Most plastic surgery practices are now run like a commercial enterprise and don't deal with things like financing. Instead they recommend patients to loan companies whom they get a kickback from.
Some small town doctors may be open to doing a plastic surgery payment plan if you know them well and have built a relationship with them. Other than that I don't know who would offer it. The last thing they want to do is have to deal with collections and hounding you for payment if you don't pay like you should.