There are several ways you can try to find a MATLAB code for Rate Splitting multiple access (RSMA). One option is to search online for open source code repositories or forums where people share their MATLAB code. Another option is to look for research papers or articles that describe the RSMA technique in detail and see if they provide a code implementation as part of their supplementary material. Alternatively, you can try contacting researchers or organizations that have worked on RSMA and ask if they would be willing to share their code with you. Keep in mind that it is important to properly credit the original source of any code that you use in your own work.
One way to find Matlab code for RSMA is to check the open source code repositories, such as GitHub, or Matlab Central File Exchange, where you can find various code snippets and ready-to-use functions to implement RSMA. Also, you can search for RSMA Matlab code in the research papers that discuss and evaluate the RSMA technique and see if the authors have shared their code.
Please keep in mind that the usage of any code you may find, you should check the license and the terms and conditions of the code usage and the citing rules. Also, it's always best practice to understand the code before using it in your own work