Below is the replication package for the following paper:
Head, K. and T. Mayer, 2021, "The United States of Europe: A gravity model evaluation of the four freedoms", Journal of Economic Perspectives 35(2): 23-48. Online appendix.
The zip archive, downloadable HERE, contains all data and code needed for replication. It includes several gravity datasets and related programmes for estimation and simulations, mostly using R. The readme file provides more detail. Please cite the above reference when using this data/code.