Hahaha..... It was some steel strip edging I'd had garage for probably....25 years ! (Think I had it to weld up some door panels on a VW beetle...but that's another story!).
Had a quick look online and you can buy it at steel stockists such as -
http://www.campsteel.co.uk/products/mesh-flooring/edging-strips/
I simply cut the edging, with 45 degree mitred corners, to make the frame 140x210 mm. Brazed the corners on one long side and the short edges. Cut the mesh to size and inserted, then fitted the other long edge and brazed the two corners, cut out the tabs that mate with the mounting point on the bottom of the rads and brazed that on.
I needed to trim down the plastic shrouds of each rad just so the guards slid in but that's easy.
Sprayed the guards - satin black... And fitted!
Oh and the bin came from Homebase!! Should have been £7.50 but I waited 'till they had a 10% off day so it was £6.75 !!!!
Cost me less than a tenner!
Or you could try Mr Hootons or ..
http://www.motorcycleparts-hornig.com/BMW-R-1200-GS-LC/Alu-High-grade-Steel/Cooler-protection.html