AFAIK large companies have deals with the government and have special units that deal with that type of content (nobody survives longer than 12 months there).

You can get legal datasets for sick pr0n or warzone stuff you would like to keep off-platform that might have the same psychological effect on you.

Should be simple enough to have the government/LEAs posses the training data and have a standard harness/workflow you integrate your training program to. Then you send your training peogram and get the resulting trained model files back.