Do-it molds makes a blank mold, http://www.do-itmolds.com/

They do not offer custom mold making, but you could do it yourself.

Janns netcraft http://www.jannsnetcraft.com/ item no. 411-145, $24.98 , blank mold.

I have made them in the past, went Boeing surplus , bought two pieces of aluminum pinned them , grind out the design, drilled a sprue and poured. Time consuming but fun.