EXCEL: Dependant data validation drop down which excludes duplicates

[Bakesy]

Hi all, this is my 1st post so hoping someone out there is able to help. Excel file is attached

Basically by browsing forums I have managed to use dependant drop downs based on data in another spreadsheet but this is showing duplicate entries (as shown in cells C6 & C7).

Is there a way to continue linking to the same data but not show repeat entries in the drop down list. I'm hoping it will only require a litlle tweeking of the current functions i've used for the data validation.

Any tips greatly received as i'm pulling my hair out here!