The Retina should be able to use standard VGA monitors without trouble, and they are often less expensive than multiscan monitors. If you get a scandoubler you can use this monitor with the standard Amiga output, too.
I haven't seen a multiscan monitor suitable for the Amiga for ages (IE one that can do both 15kHz and 31kHz+).
There was a 17" monitor from Sony I believe which had TV capabilities, and thus worked both with high VGA/SVGA resolutions and the Amiga video output. I'd check the eBay or something similar. I think it was launched in 1997 so my bet is that it's out of production.
If you really do want a multiscan monitor, the main thing to make sure is that it is capable of handling 15kHz vertical sync, otherwise you might as well go for a standard VGA monitor. The second thing is that it stores the settings digitallay. The 1942 has analog knobs which is a pain in the ass when switching between lots of different resolutions.
If you've got the desk space, you could keep the 1942 for your Amiga output and buy a VGA monitor for your Retina. This would also give multitasking a whole new dimension. You could for example run Term on the 1942, watching the progress bar while working in another program that runs on the Retina output.
