Originally Posted by
beergut
VAT 407 is only available to the retailer, they have to order them from the VAT office ...
... and they need to supply their VAT registration number when they do. It's not something you can fake, even if you're willing to con Her Majesty's Revenue and Customs. After a retailer orders them, I suspect they normally come by post, so allow another couple of days to get them in the mail and for them to arrive.
That said, if you're buying enough stuff and give them some notice, a merchant ought to be willing to lay in a supply. The forms don't cost anything.