Saskguy - the first thing to do is to slug your bore to find the bore and more importantly, the groove diameter. With luck you may find easy to procure moulds will be available from RCBS or Lyman.
If a custom mould is necessary, I'd first look to LBT moulds made by Veral Smith. Do a google if necessary. If a custom mould is necessary, lookhim up. The reason I prefer him as the mould will cast the diameter he says it will, from the alloy you specify. If you buy form NEI, you'll be taking a chance with a mould you probably cannot return. LBT moulds cost about the same or a bit less than most other custom moulds. RCBS has a fairly good line of various sized .40 cal moulds.