Hi,
Microvitec produced a range of Amiga-compatible multisync monitors that were popular in the UK in the 1990s (some were actually re-branded by Commodore and Acorn, amongst others).
It appears Microvitec still makes this style of monitor. Have a look here on
Microvitec's web site and check out the Desk-Scan 1402. Only a 14-incher, but will do all the classic Amiga and A1200 screenmodes.
Alternatively, you might have some luck with certain LCD TFT displays. Some of these may sync down far enough...
- Ali