I can give you a step-by-step method that is one of the many ways to get the Aureus Scandens, but you might have to keep buying common seeds from the shop to get the ones you need to start with.

Cross a Jalapa Astera with a Fourpetal Reptans (or a Fourpetal Astera and a Jalapa Reptans) to get a Fragrant Grass.
Cross the Fragrant Grass with a Citrus Reptans, and you'll have the Aureus Scandens.