I found a draft copy of "ACP DOCUMENTATION GUIDANCE
FOR PROJECTS OUTSIDE THE U.S." from 2011. It explains how to document MR c5, including downloading the "ACP Regional Materials Calculator." In another LEEDuser forum (also from 2011) the question was asked "where do you download the calculator from", the answer was from the Resources page at USGBC.org. Just checked; the calculator isn't there, and I can 't find a non-draft copy of the above referenced document. Have the documentation requirements changed since 2011? What are they now?

UPDATE: After a bit more research I've found out that this ACP is not an option for CI v2009 projects, although it looks like it may be available for CI projects under LEED v4. It is available for v2009 for NC, CS, and EBOM projects; there's an option on the credit form you can check if you wish to use it.