How to do a Vlookup without knowing the column number

I have a spreadsheet that I currently use to track the total revenue for a variety of different products. The data is pulled from a Pivot on a different sheet that is updated daily. I currently use VLookup to pull this information by matching the ItemID (Column A).

Here is my problem: I need to add the monthly revenue for each month after a product is released to this spreadsheet. Unfortunately, each product has a different release date so I can't tell Vlookup an exact column number to search for the corresponding data.

Is there a way I can do a conditional statement or something similar instead of giving an exact column number in Vlookup? For example, have it look for the first column that contains data and return that as Month 1, and so on for month 2, 3, etc. If not, can you think of any other way to set this up? Also, please note that some months may have 0 revenue, which will need to be included as a value, not skipped over.

I have attached a sample Workbook that is modeled in a similar way to the actual spreadsheet I am using, except MUCH less data and using a static table for the source data instead of a dynamic Pivot table. Does anyone have any idea how I can populate the month revenue from the 'Source Data' sheet? Please note that the actual spreadsheet I am using has the Pivot table refreshed daily with updated information and there are new products added all the time so the information never stays in the same column or row #.

P.S. On the 'Source Data' sheet you will notice that the Year and Month headers are on separate rows, unfortunately I can't alter this (DB is read-only) to have them combined on 1 line (e.g. Dec. 2012, Jan. 2013, etc), which means I can't look the column up by matching the Release Date to the corresponding Month & Year.