Lookup Nth Occurrence Or Instance

I have a very very long weekly table of, say, sales regions, items sold, revenue, profitability, etc.

(Very long here means 120,000 rows, and in Excel 2007 - please don't hold this against me! )

Let's assume Row 1 and Column A are for headers. So Column B is Sales Region and Column C is Item Name. The first Sales Region, beginning in B2, let's call it "America", will repeat (B3, B4....) until the Item Names are done for that region. Then the next Region starts, "Australia", and the list of Items starts again, etc.

Not all the Items will be sold in every Region each week, and even some Regions may disappear from the table one week only to reappear a few weeks down the road. The table is Sorted alphabetically, though, first by Region, then by Item.

One way to VLOOKUP week over week information from last week's report onto this week's report is to concatenate both weeks' Region and Item information (=B2&C2) seperately, and VLOOKUP by that. This returns only combinations of Region/Item that occured in the current week, and with ISERROR, 0 for combinations that occured this week, but not last week. As far as what it returns, this is fine for our purposes but with several pieces of information to VLOOKUP (#, revenue, profit, etc.) and 120,000 rows, it takes forever. Literally over an hour to copy down the week over week parts.

I had the idea that maybe it would be faster if I could define individual VLOOKUP ranges for each Region, and then look up Item within that range. These ranges would vary in placement in the table and in numbers of rows each week, as the number of Items sold in each Region waxes and wanes, hence "dynamic ranges" - I hope I've used that term correctly.

Is there an effective, efficient way to return the row numbers of the first and last instances of a given Region, and use that range for the Item VLOOKUP?