Only just found this - sorry for the delay guys.
This is exactly the kind of gear we have on the shelf.. if anything our gear is a little overbuilt for this purpose but what the heck.. when was that ever a problem
Looking at about £30 depending on exact unit.. for a clamp with 2 threaded bolt holes... I can supply the screws FOC all you need to do is drill through the flag pole (or similar) to mount it on there nice and firmly.
Anyone interested give me a bell on 01270 872161 and I'll do my best to sort you out. All pricing always include next day overnight delivery and VAT