You could search for oval mat cutters.. 

heres one I did earlier..
'http://www.logangraphic.com/product/handheld-mat-cutters/logan-201
-oval-circle-mat-cutter/">http://www.logangraphic.com/product/handheld-mat-
cutters/logan-201-oval-circle-mat-cutter/

complete with angled cut.  It’s seen in use here..    Nothing like as impressive
as a real brass affair though..


https://www.youtube.com/watch?v=HIoL0SA-91M