Available from retailers like eBay or specialized hobby shops like Super-Hobby , which lists similar Polikarpov models.
Sites like AeroFred and Incredible Adventures offer free downloadable files for various Polikarpov models, though they may not be the specific "Fly Model 039" edition. Download Fly Model 039 Polikarpow rar
Be cautious when downloading ".rar" files from untrusted sources, as they can sometimes contain malware rather than the expected model plans. Available from retailers like eBay or specialized hobby