As has already been mentioned, there's not a lot of choice over here when it comes to kaiju films in any format (unless you're big into collecting old VHS tapes
). I think Shin Godzilla might literally be the only actual Blu-ray release of any sort of film like that in the UK, Godzilla or not, apart from the US Godzilla's of course. A region-free Blu-ray and/or DVD player really is a must if your friend wants to pick up more than a handful of titles (my entire collection is made up of Sony, Classic Media and Madman releases, plus a few of the more recent Blu-ray imports).
That being said, the Godzilla vs Biollante Blu-ray is another one that hasn't been mentioned yet that's definitely region-free. It could make for a good double feature with the G'84 Blu-ray, since like Dai said that's region-free too. The Madman release of Shin Godzilla is also region-free if you or your friend happened to prefer the special features on that above those of the UK version, but since that's one of the rare Godzilla films that's actually been released over here it's not at all necessary to import it.
But yeah, I think all the US and Australian DVDs are region-locked, though if his Blu-ray player plays multi-region DVDs as standard then there's plenty of choice available there, which might be the easiest option if that's the case.
Sadly I feel like the potentially upcoming Criterion Godzilla films will be region-locked though, just as their release of G'54 was. I'd love to be proven wrong, but I'm not getting my hopes up too high.