Delta has a seriously good fare with plenty of availability from SFO to LIM but also other airports notably:
This fare also works one-way from North and South America.
You can book directly at delta.com. I just booked a one-way for myself to Lima the Monday day after Thanksgiving 🙂
The fare earns 100% miles on Delta Skymiles and Alaska.
Book this one if you are interested. Delta.com has a 24 hours risk-free cancellation policy if you have doubts later on. The purchase will be refunded to your CC.