RRC is right. After building your project there is a “work” folder in the project directory. In there their is a “verilog” folder with your converted source files.
You can also open the Vivado project directly in Vivado if you want. The file is in “work/vivado/PROJECT_NAME/PROJECT_NAME.xpf” where PROJECT_NAME is the name of your project.
Just note that the entire “work” folder is deleted when you build your project. If you want to work on these files directly you need to copy them somewhere else.