Thanks. They look virtually impossible to buy in the UK or on eBay from the Far East though.
Have you tried dancap.co.uk?
Assuming you've no luck in Europe or the UK, you could get them from the US as a last resort.
TEquipment still has them for example (
here), and they will ship internationally.
I mention this, as I've seen a notice that the T18 series is going to replace the 900M series, and when I checked Hakko's site, there's no T18 series drag tip with a well in it. Just smooth bevel shapes that you're not happy with, and others of course (they do offer a knife, which also works for drag soldering).