You could contact Anders Hellburg in Sweden, who runs the GR-3 registry (anders.hellburg@scuderiadetomaso.se). There weren't many factory Gr-3s (maybe 35) because the parts needed for an FIA Gr-3 could be bought piecemeal from DeTomaso and added to a GTS at home, or ordered with the car from the factory- but if you didn't get them all at purchase, the factory didn't log it as a GTS-GR-3. A few buyers didn't want everything because they were only buying a faster-than-normal street car with no pretensions of ever pro-racing it. And of course, some were later upgraded by the factory to GR-4 (one to GR-5) specs.
The known Gr-3s are also listed in P. Olczyk's 2006 book 'DeTomaso- Macchina da Corsa: A Racing History'(462 pgs with photos of nearly all the factory racing cars).
