Where can I find gray LCD (like the one in a calculator)

Using Arduino Project Guidance
6

http://www.ebay.com/itm/8-DIGITS-7-SEGMENT-LCD-DISPLAYS-GLASS-2-PCS-/320778989149?pt=LH_DefaultDomain_0&hash=item4aafeaee5d

They are not really easy to interface. They have loads of (possibly multiplexed) lines.
You will need to expand the output ports or get a controller IC.