If I were making a secure file request/dropoff operation, I would host a chat room on a TOR hidden service where you could ask for the material in question, and

If I were making a secure file request/dropoff operation, I would host a chat room on a TOR hidden service where you could ask for the material in question, and a separate file server where you could upload the file. There would be a client that encrypts the file client-side and uploads it to the service and a client that downloads and decrypts. The uploader would post a link with the key to the forum after uploading. Once the file is downloaded, it's deleted. The two services would share no data with each other and appear as two completely separate services. Of course, then you run into the problem of having to moderate the thing, since you don't want to become a facilitator of child pornography etc.