Thanks for the link. Looks like they only do 50cm (although they may stock more - just not on the website).

I've just ordered from Moddiy which is a USian store, so the airmail is about $8 on top. But it still works out cheaper than the best UK deal. I found a site that sells one right angle 20cm plus one straight 20cm as a pair, which is sort or weird. I'd have to buy five packs at nearly £5 each an then have a load of short straight to straight cables I don't need.

It's a bit frustrating. I'm not wild about cable management, but I like to have the case so I can actually get at stuff when I need to. Also, with that many big HDDs, it's important to have some cable-free space for air flow. But this side of the pond even ebay is a let down.  

Ahh, I'm not the only one with a big case full of disks then (5 HDDs and one NVME SSD in mine). To be honest, one of my biggest bugbears with modern motherboards are the side-mounted SATA sockets. Makes plugging in the cables a royal shit when you're crouched over your case with about 1" of room to spare between the motherboard and other parts of the case... 

It's really tough on these microatx boards.

Absolutely! My last case was too small really, but one "feature" was the rolled lip on the plate the mobo mounted on. Saved cut fingers but just overlapped the stupid side mounted SATA sockets. They could be fitted but what a struggle when you can't get your hands in and the cable's too long anyway.