Salvia subrotunda is similar to Salvia coccinea; the seeds are very easy to plant and germinate. Unlike Salvia coccinea, Salvia subrotunda is much taller (in our climate, approximately 4 to 5 feet) and its flowers are shaped differently than Salvia coccinea. The flowers tend to last for only one day and then fall off of the plant.
This has reseeded for us. In fact, with the mild winter of 2018, we had a bumper crop of Salvia subrotunda.
The only source for plants was Flowers by the Sea, but they are out of business. There is a seller of seeds on eCrater.