I ended up making myself a set for the OT and a set for my MnM.
No disrespect intended to Pro-Modular - it's just that being in the UK, 2 sets + shipping + customs/Tax sting would've probably ended up about £50-60.
Luckily for me there is a plastics shop in Coventry which is not a million miles from me and they sell A4 off-cuts of 3mm Perspex.
If you've got a jigsaw, a workbench, a couple of clamps, a couple of files and a steady hand they're not too difficult to make. I did get help from my wife - she managed to make a vector drawing template that I cut out and stuck to the perspex as a cutting/drilling guide.
I made mine slightly taller than the Pro-Modular ones too so that the front edge of the unit sits higher off the table.
Although obviously mine are not laser cut like the Pro-Modular ones: they're more like analogue cover-versions of the Pro-Modular cheeks. The test will be when I get the screws to fit them.