From what I've seen, they're planning on opening back up for orders tomorrow (May 2nd, 2021) so I'd check back then.
But if you don't have luck with them, the good news is pretty much any cable capable of carrying RGBs that has the H-sync line connected to SCART output's sync line will do.
The cables are just sets of conductors with no other components other than (usually) a resistor on the sync line to keep the voltage of the sync signal in check. They don't care about region, sync type, etc; there's nothing in them but metal. PAL vs. NTSC also doesn't matter in terms of cables for your MiSTer either. Other hardware (PS1 or modded N64 is a good example) might have more particular requirements built into the cables, but MiSTer is as simple as it gets IMO.
What exactly are you outputting to? If you're playing on a PVM, you could just get Monoprice's HD15-to-BNC cable.
https://www.monoprice.com/product?p_id=566
They're reasonably well-made. The H-sync line is used for Csync on MiSTer (as well as Analogue's consoles.)
If all else fails and you're feeling like doing some DIY solder work, you could also consider getting a cheap male-to-male SCART cable, hacking it up with a VGA cable and an AUX cable and making your own. This is what I basically do and I haven't had much issue. The MiST project's design works fine for me:
https://github.com/mist-devel/mist-boar ... ScartCable I just leave SCART pin 16 (RGB switch) disconnected because it's really not useful for me since I don't have any analog equipment that would make use of the RGB auto-switch signal.
I've also taken cheapo component RCA cables I got from a thrift store and hacked them together with a VGA cable to make a sort of budget 5 BNC type thing, since I already keep RCA-to-BNC adapters plugged into my PVM.