How can I locate someone in the Federal Prison System?

I recently received a note from my half-brother’s wife, informing me that he’d been convicted of a pretty serious crime and would be sentenced shortly to 5+ years in a Federal prison. I’d like to send him a letter, and maybe a care package. Unfortunately, I can’t seem to get in touch with his wife or his mother to find out where he was sent.

We aren’t terribly close, so we hadn’t been in touch much in the recent past. Not thinking I might need it, I threw away the envelope the note came in. The last phone numbers I have for them and for his mother are out of order, and I haven’t been able to find any new information on them. Since I can’t find either of them, my last resort is trying to track down my brother through the prison system. If it matters, he lived in Virginia at the time all this took place, though I’m not positive that’s where the crime/conviction occurred. Any advice?

Note: I don’t mind if this goes off-topic a bit, but please do try to be helpful. Thanks!