index match remove duplicates

In the attached workbook I'm trying to create a drop down list (D2) to return matches to Skew (C2) without duplicates, from array C5:D3240.
Any help or suggestions would be greatly appreciated.
Sick

I'd say start with creating a list of unique values. In E5, let's put this:

=IFERROR(INDEX($C$5:$C$3240,MATCH(0,INDEX(COUNTIF($E$4:E4,$C$5:$C$3240),0,0),0)),"")

...and copy it down until you run out of values. Then, for your data validation formula, use this:

=OFFSET($E$5,0,0,COUNTIF(E5:E48,">0"))

I realized I misunderstood your question, give me a moment to work out a solution.

Have you considered using filters of a pivot table for this?

what do you mean by OFFSET matches?

OK the more I look at this, the more it confuses me.

Perhaps this in I5...
=IFERROR(INDEX($C$5:$C$3240,MATCH(0,INDEX(COUNTIF($I$4:I4,$C$5:$C$3240),0,0),0)),"")
then J5...
=VLOOKUP(I5,$C$5:$D$3240,2,0)
both copied down

If this is not what you want, please shopw expected outcome

Try this in E5 instead (it is an array formula, so confirm it by pressing CTRL+SHIFT+ENTER)

=IFERROR(INDEX($D$5:$D$3240,MATCH(0,IF($C$2=$C$5:$C$3240,COUNTIF($E$4:$E4,$D$5:$D$3240),""),0)),"")

EDIT: and then use this as your data validation:

=OFFSET($E$5,0,0,COUNTIF(E5:E48,"*"))