Which calcium salt is good enough to make calcium benzoate?
Thanks to @Shoubhik who pointed out that calcium hydroxide is good enough to make calcium benzoate. To support this claim, I found a patent which indeed describes that calcium hydroxide was used to make calcium benzoate (See comments). Here is the summary of the patent: 


  The invention relates to a processing method for synthesizing calcium
  benzoate at low temperature. The method comprises the following steps:
  heating and stirring 65-85kg of industrial-grade benzoic acid, 28-32kg
  of calcium hydroxide, 1-3kg of catalysts comprising triethanol
  distearate, ethylene distearamide and ethylene bislauramide and
  300-500kg of clear water in a reaction kettle at 333-363 K to react
  for 2-4 hours; and then adding 5-15kg of separant, stirring for half
  an hour, filtering and drying. The method provided by the invention
  can be used for directly synthesizing calcium benzoate, thereby
  lowering the equipment investment, reducing the working procedures,
  lowering the labor intensity of workers, increasing the output,
  enhancing the quality, lowering the cost and preventing the
  environmental pollution.