External Data Update Until Last Day of Month

I have a spreadsheet that uses external data to populate commodity price fields and it works (CBOT and CME). In addition to pulling in future prices, I would like for the program to retain the prices for the last trading day of each trading month. As is, the program copies the last price backwards to populate history (on the Summary tab). I canot find a table on the web with last trading day price history. I have messed around with some VBA but do not know what I am doing and am stumped as to a solution - any and all suggestions welcome.Commodity Prices swine tpk april 2013 vba.xlsm