Thanks for all the replies. I'm in the Netherlands, where Surly LHTs (used or new) are rare. But good condition, classic steel Koga Miyata mtbs can be had for around 200 euros.
Santos is another local builder with an excellent reputation & lots of good-condition frames available. The SCC 02 is also around 200 euros, & looks almost identical to their renowned Travel Master 2.6 (one of the most popular adventure bikes in the world). But it's alu, & has modern sloping geometry (I think I'd prefer a more classic style).
I will keep an eye out for rigid Zaskar & Backwoods. At the moment, only hardtails are available.
The most easily available bikes are, not surprisingly, mid-range models from the big names: Trek 900 series, Cannondale (S)M 800s, & the previously mentioned Rockhopper.
From the 5-arm cranks & quill stems these appear to be a little earlier than the late 90s, but are these the model Rockhoppers you had in mind?