So, in my study, I've got some twin-slot shelving rails (specifically B&Q's "flexi" system), with shelves on, as normal.

Now, I'd like to mount some stuff (power strips, etc.) in the same plane as the wall, so I'm thinking that I can mount some fibreboard vertically to the upright rails, spanning at least two rails, preferably so that it mounts into the existing slots in the rails.

But, I can't figure out whether this kind of bracket is available, how to search for it, or -- if it's not available -- how to mount something like that myself.

Ideas?

This BBS is brilliant! Immediately after posting that, I found something like what I want. Thanks, BBS!

Now to figure out if (a) this is compatible with the B&Q system or (b) if there's something similar for the B&Q system.

So now you just need to measure the pitch on your existing units.
Edit:Though in this case I suspect it really doesn't matter: they should fit and work fine.

I've ordered some. Worst case, I can just file them down a bit.

They do. Sorted.