Just having a bit of a google for you.
This one will cut metal as its HSS. Its 83mm but the 0.5mm per side shouldnt matter.

Its £11.93 of ebay
There is also this adjustable one but its not cheap:

Its £64.57. It says it will cut sheet metal up to 1mm thick, im not sure how thick your CP is.
Worst case scenario if you send your CP to me I could circle interpolate the hole for you at work.