You should be able to get the std.(i.e. non autostop) fill valve at any
reputable propane/appliance store/repair facility,as well as any RV
facility. It is the same as is installed on larger tanks for home use. If he
is changing from an autostop valve, you will also need a bleed tube/valve.
Most of those come with a section on tubing attached,which will need to be
cut off for the bleed valve to fit the Westy tank. Just toss the tube that
originally connected from the autostop up to the top of the tank.  I've done
all my vans in the past this way,it's the best and cheapest alternative.
Should cost around $30-40 for the parts. When installing them,I use a white
liquid teflon sealant that the store should have also.

Karl