Tesla's "Gigafactory" currently has just the assembly line for battery packs that used to be in Fremont. LG's factory in Holland, MI is the largest battery factory in the US and is set up for easy expansion.[1] The Chevrolet Division of General Motors has a good track record at manufacturing large numbers of cars. They can probably make as many as they can sell.

Tesla is still learning how to scale.

[1] http://www.autonews.com/article/20151214/OEM06/312149992/lg-...