Can anyone recommend a resource for monthly trade data for Mexico from before 2010? Can anyone point me to a resource where I can find monthly series data (specifically for 2003-2013) on Mexico's imports and exports in nominal (current) Mexican Pesos (MEP) including broken down by major industry?

I've found UN data and OECD, but am having trouble navigating the INEGI site (since my grasp of Spanish is limited to the colloquial).
I had a look for a few places. Looks like the WTO have something relevant. I haven't looked at the dataset but hopefully it is useful. This only has annual trade. The World Bank also has some data also covers annual data.

http://imts.wto.org/CDS/gp/tsselection.aspx

I think this one has your answer. It has monthly data. Only 1000 records at a time but up to 5000 if you sign up. You will probably have to be a bit clever with your queries and then merge a few spreadsheets as well. Clunky interface but the data looks vast.

http://comtrade.un.org/monthly/Main/Data.aspx