Collaborative screenwriter

I am an independent producer. Right now I am looking for a scriptwriter to collaborate in the production of two feature films. The plot of both feature films is fully developed and the projects have been agreed with distributors and producers. The idea is to be able to reach an agreement with the scriptwriter to agree on a payment after the sale of the script and over time create a joint work network. The scriptwriter will also be recognized as a creator. Preferably that the scriptwriter speaks Spanish.