If it were up to me, I would not set up your sheet the way it is. But as you have things set up, try this formula in B8:
The formula uses curly brackets to form a virtual array with the A2:A5 values concatenated with C2:C5, and to the right of that (in memory), the values from B2:B5. Underneath this array (as denoted by the semicolon), another array is formed with the A2:A5 values concatenated with the E2:E5 values this time, and to the right of that (in memory), the values from D2:D5. In the end, this array will contain just two columns: the first with the concatenations of every rows model with each possible vendor for that model, the second with the correlating size for that pairing.
VLOOKUP then concatenates your selected model and size from B7 and B9 and looks for it in the virtual array above. If that combination is found, the value in column 2 of the virtual array will be returned. If it is not, the
IFERROR will return "NO MATCH."
FALSE in the
VLOOKUP means "My results aren't in perfect ascending order and I'm looking for an exact match only."