Order through Amazon for a generic reamer rather than a fencing equipment store. It's the exact same thing, but a little bit cheaper. Can't remember the radius, though so you should check that.

Edit. Just checked. I got a 4.5 mm hand reamer from Amazon for about a fiver (£). I'm thinking I might put together a toolkit guide.

www.amazon.com/gp/aw/d/B00REGVU5M/ref=mp_s_a_1_1?qid=1449758492&sr=8-1&pi=SY200_QL40&keywords=hand+reamer+4.5&dpPl=1&dpID=31PaA5lmOZL&ref=plSrch

This should work