This is a 3 chain system. It is the current standard on new ELFs. The motor and geared hub (often an Nuvinci CVT) are mounted under the seat. The sizes of the cogs might vary. There are 3 bolt on cogs in this design. They are not very common bicycle parts, but most bike shops can order them. They appear to be Problem Solvers cogs. (note the picture on the Problem Solvers page shows the cog with an adapter that is not used on the ELF)

The motor connects to the right side of the rear wheel with a 3/32" chain. The rear wheel has a 22 tooth ACS Crossfire freewheel on it. The cog on the motor is a 18 tooth bolt on cog.

The mid drive geared hub is connected to the left side of the rear wheel with a 3/32" chain. The rear wheel has a 20 tooth bolt on cog and a spacer to keep the chain away from the rotor of the disc brake. The chain is goes to an 18 tooth bolt on cog on the left side of the Nuvinci. There is a spacer between the cog and the nuvinci.

The right side of the Nuvinci has a 18 tooth threaded cog with a 3/32" chain that goes to the pedal chain ring. I don't know how many teeth the chain ring has yet.

This is a work in progress based on scattered info collected from the ELF Owners group.

In the pre-updrive configuration the motor is mounted under the seat. And it has a 1/8" chain to the left side of the rear wheel. I believe the chain model was: Connex 1R8 1/2 x 1/8 Nickel Heavy Duty

The motor has a 12 tooth cog on it. Perhaps like this: http://www.bikeman.com/FW4752.html

The rear wheel has a left side freewheel, most freewheels are mounted on the right side. So this left side freewheel is hard to find.

The pedal chain goes all the way back to the rear wheel which has an internally geared hub in it.