The mini sketch pencil will take both 3mm and 3.15mm leads.
3mm refills can be found at Drawing and Drafting and from 043 Turning .
The 3.15mm leads can often be found where Worther Shorty, Peter Garrick Stubby, Lamy and other sketch pencils are sold. Try places like NoteMaker.com.au. They offer a range of colors in the 3.15mm refill.