Spoiler
They were de-kilted in 1809, so you shouldn't have one if you want them to match time period of the other British troops.
Indeed, but it's going to be even harder to find images of the 75th without kilts so we'll keep to the kilted time period.
Images;
Private soldiers
Spoiler
this one doesn't seem to have the cap feathers for some reason however.
Private of the Gordon Highlanders;
However this is what we would like the British Riflemen re-skinned to, if that is possible;
Ensign (kings colours)
A drawn picture (not sure how much you can get from this)
NCO Uniform (not sure how accurate the badge on white pouch is)
badges/plates
Spoiler
this is helmet plate
this is quilted shakko badge
Officers badge
buttons
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normal (but later than napoleonic era)
officers^
Again James Grant's picture but formatted without the 76th;
And therefore the tarten;
Spoiler
EDIT: This is the Tartan which that image shows, however I have found evidence suggesting the tartan is in-fact the one shown in post below. I will talk to Lime about the more historically accurate one.
I can find more stuff, but dont have the time yet, hope this starts to help and there is quite a lot of 75th stuff if you dig deep