VLOOKUP with two variables

Hey, I am trying to create a Vlookup sub in VBA. I'm fairly familiar with regular formulas, but VBA is something new to me. What I have is an inventory sheet that contains and items NSN (serial number), component number, item name, and allows me to punch in the totals. I have it set up already using Vlookup to autofill the item name when I punch in the NSN. However, I want it to be able to do the reverse as well, lookup a NSN when I punch in the item name. The reason being some items have an NSN, but don't have a common name. Or sometimes an item will have a common name, but won't have a NSN number because it is no longer in the original packaging. So I need to be able to do both. The way it is set up now, it is an inventory sheet with approximately 23 worksheet pages, that will total up every item on the last page. Each item reference comes from a separate workbook, that contains the master list of all items, NSNs, and Component numbers. The current Vlookup formula references and pulls its data from the mastersheet, which is what my VBA sub will have to do. Any help would be appreciated, since I am very new to the VBA system.

:also attached are the excel sheets I have been using.