INDEX MATCH For Repeating Lookup Value

So I have values in two colums like so -

A

aluminium
steel
plastic
aluminium

[Code]...

I now have another worksheet wherein I want a cell to recall a Value from range "A", using the code in range "B". So for example I'd want want my cell to search for the code to the left of it, "6464", and bring up value "Aluminium". HOWEVER, and here is where I feel it gets tricky - I intend to drag that cell down across a column - but when the cell encounters "6464" again, instead of showing "Aluminium", I this time want it to show the next entry under "6464" - "steel".

I hope this is clear. I'd post the excel spreadsheet but it is very large. Basically I want to INDEX MATCH function to remember its already recalled a specific value for code "6464" (in this case "aluminium") and to recall the the OTHER value related to this code.

My excel has a range of Purchase orders, and a range of the materials ordered under that PO number. I'm making a sheet that drags out all the PO numbers from my worksheet (which will have repetitions of 4-5 at a time), and then using those POs to find each material ordered that corresponds to that number.