Check out ebay.it. Managed to get a brand new Givi one (340F) and monokey plate (M3) for £65 delivered. Loads of shops on there stocking it, some will post to UK, others won't, just send them all messages. Mine was from an ebay shop called 'Motopui'. Most of them speak enough English, so no worries there. And don't worry about duty/vat, being in the EU there's no hidden costs. Either way, it beats many of the crazy prices they go for second hand on ebay over here. When I was looking, most ended early before I could even bid, guessing someone just offered them cash up front. Plus buying new, there's no worries about all the bolts and stuff being included.
Otherwise, just order the bars (340F) from Italy, then source the M3 plate locally, as this is pretty common and fits many different bikes. Just make sure it comes with the silver metal brackets to fasten it to top of bars. I then picked up a second hand box local off ebay uk. Got an old E50 Maxia one for £57 quid.