It seems that retrogamingcables.co.uk made a RGB SCART to VGA cable for use on the the Extron scalers a while ago (not sure if it would work directly on a CRT monitor though), but now there's no mention to it in the website store:
https://www.videogameperfection.com/201 ... le-review/But you are looking into a more complex situation than just a simple adapter. Non-VGA games output video at 15,6 kHz, whereas VGA games output at 31,2 kHz. The problem is, the vast majority of CRT monitors don't support 15,6 kHz inputs, so your monitor most likely will not show any image or rant about the input signal being out of the scan range.
I'm in the same boat as you. I have a Sony Trinitron Multiscan CPD-G500 21'' CRT Monitor that has dual inputs (VGA + RBGS BNC), which I use for both my computer (VGA) and Dreamcast (BNC via a SCART to BNC adapter - Toro does 480p through SCART). It works with VGA games as it should, but doesn't work with non-VGA/31,2 kHz games.
If you really want to play non-VGA/31,2 kHz games on your CRT monitor, your solution is to use a scandoubler aka line doubler or upscan converter. For now, the most used options are: the CGA to VGA scaler board that uses the GBS-8220 chip (cheap solution) or the Framemeister (expensive but better solution). The OSSC board also does this job but it only outputs through HDMI (digital output) and lacks analog output, like VGA.
If you don't want to spend the cash on a Framemeister, your best bet is the GBS-8220 board, but it only has VGA in/VGA out - it doesn't have SCART input or output for that matter. Fortunately, fagin from the shmups forum has already modded his board to accept SCART:
http://shmups.system11.org/viewtopic.php?f=6&t=35423 (you can see in the last page that I made a post asking the same thing basically).
That being said, I found this cable SCART to VGA cable (please read the description, specially the note):
http://www.maplin.co.uk/p/scart-to-vga- ... able-a38bfIn conclusion, most likely a simple SCART to VGA cable adapter won't work, and you'll have to get a scan doubler to play non-VGA games on your CRT monitor.
For more info about scalers, scandoublers and whatnot, check fudoh's webside:
http://retrogaming.hazard-city.de/