Standard/Specification for regular alkaline batteries
Where can one find the standard specification for regular alkaline AAA, AA, C and D batteries?


The international standard is IEC 60086, specifically:
IEC 60086-2:2015 - Primary batteries - Part 2: Physical and electrical specifications
(current cost is CHF 250)

Abstract:
IEC 60086-2:2015 is applicable to primary batteries based on standardized electrochemical systems. It specifies the physical dimensions, the discharge test conditions and discharge performance requirements. [...]

Examples of IEC battery type designations include:  


alkaline AA = LR6
alkaline AAA = LR03


Other IEC battery designations are given in the Wikipedia article on battery sizes.

(I believe there is an ANSI-equivalent to this IEC standard, but I haven't used it.)