Dependant drop down data validation using unsorted lists

[Lonemascot]

I have a problem trying to create a data validation list from matching data in an adjacent cell to an unsorted 2 column list on another sheet.

First sheet - Reference column A to return column B

	A	B
1	ROOM	ELEVATION
2	Study	Rear
3	Living room	front
4	Study	Rear left
5	Dining	Right
6	Dining	Front right

<tbody>
</tbody>

Due to the nature of this sheet it is not practical to sort the ROOM column

Second sheet

	A	B
1	ROOM	LIST OF WALLS
2	Study	Rear Rear left
3	Dining	Right Front right
4	Living room	Front

<tbody>
</tbody>

Eg. The data validation list drop down in cell B2 should firstly look at A2 and then go to sheet one, look down column A and all the cell contents that match with Sh2 A2 populate my list. i.e. The list should only contain “Rear” and “Rear left” as options.

Had column A in sheet 1 been sorted then I could have used a combination of OFFSET, MATCH and COUNTIF to return my list. I'm at a loss to find an alternative solution on unsorted data.

Any help or pointers would be really appreciated.