Yes, you can get the Denso Supra from the All-Japan GT series in Amateur. The other choices are the Arta NSX, the Calsonic Skyline, and the Loctite Skyline.
I don't know what differences there are between the Denso Supra and the Tom's Supra.
Welcome to GTP, Finnman! What are you using in this series? I just completed it last night - check the GT3 Writeups board for my account of the run.