If you watch his lives, he frequently alludes to his sources.
Most of these influencers WANT you to know their sources. Vig Steve has an entire "sources" section on his personal web site. Go check it out.
There are long standing sources that do fly under the radar. Closed TGs, and closed email only sources. They are something common in IFBB circles. Ive even been able to use one. Guess what? It was just some home brewer who knows the right people and overcharges. Ive had better quality by a mile from open sources from SST and here. Why? In my opinion, "public" accountability.