I can't find any square or rectangular plastic extrusions in Europe anywhere. The fence posts nowadays seem to have a slot to accept the railings. I have tried the conservatory websites, DIY centres, PVC window companies, industrial plumbers supply, and every google permutation I can think of. Ideal would be rectangular box section in 1250x1500 (5x6) or anything close really. 6x6, 5x5 - ABS or PVC. Does anyone know where I should be looking?