Theoretically you can't buy region-free DVD players because this breaches licensing agreements. However that doesn't prevent retailers selling single-region players and providing you with the hack at the same time. (In most cases, hacking a player is no more complicated than opening the disk drawer and entering a few digits on the handset).
Thanks for the responses. I hacked my last player without difficulty, via the remote, but it now lies dying (for unrelated reasons). New ones I've investigated seem either unhackable, or it can be done only with a chip and a soldering iron, which I am not about to attempt. Handsets are moe my thing.