Just an email sent to James or Grant Cooper will do the job. Their email addresses are on their profile.

Most roboteers use 75mm or 100mm wheels - these both come with special nut inserts to allow them to be screwed straight onto a drills output shaft (or are available without the nut). Less common but still optional sizes are 63mm and 125mm. Again, as far as I am aware, these both come with the nut insert too