Using Macros to monitor stock

Hi there,
We have two spreadsheets. One we use to import into our website and one from our supplier which has stock details on.

What I would like to do is have a macro which copies the product reference from our spreadsheet (catalognew.csv) and find it in our suppliers spreadsheet (products.csv) and copy the amount they have in stock into our worksheet.

I can work out how to do this for one product but I would like to figure out how one macro could do it for a whole load of them. Attached is the sample spreadsheets.