There is no description of what the Ionian sharpshooters (Septinsular company) looked like. In the battle of Peta, it is recorded that a Septinsular company took place. It is also referred that they were "regulars". So, It seems that some of the men were veterans(!) of the septinsular army.
The septinsular army created by the Septinsular (seven islands) republic (1800-1807) wore a french like uniform, similar of the chasseurs. By 1807 the seven islands ceased as a perublic and returned to the french. The British campaigned against them but French kept Corfu until 1814.
The First plate shows some roumeliote or "albanians" (christian speaking albanian, maybe souliotes or so) and the second plate is a member of the British raised Greek light Infantry . Both of the regiments disbanded by 1814.
1.- The Greek light infantry uniforms were similar to the traditional Greek dress , i.e. fustanella etc. (BTW the only surviving parts I know is the helmet and the insignia retained by Kolokotronis and still surviving at the National (Ethnological) Museum).
Since it is quite similar to the fustanella tradition dress , it is not easy to distinguish it from the dress of the Peloponnesians or the traditional dress from Rumelia.
2.- The septinsular army had French chasseurs uniform. In the area there might be left some veterans of the Chasseurs d' orient regiment, who fought in Parga during the napoleonic era. This regiment included Greeks, too.
3.- The Ionian/Spetinsular traditional dress is not like the tradiotional fustanella dress. Islanders and maniate usually wore vrakas of blue colour.
So, the speculation could be that the Septinsular company (I wouldn't dare to call them sharpshooters) could wear anything.
From miltary leftovers of french origin, to civilian clothes (i.e. traditional fustanell, vraka, breaches or Western pants/trousers).
For sake of uniformity and in order to distinguish this unit I would use figures, like Napoleonic French in campaign dress, shirts or various jackets - some in French Napoleonic coats- one or two in shakos and a couple in bicorns and the rest with fez or straw hats. pants of white or blue colour and most jackets in blue. shirts always white. The unit should Carry Western rifles (maybe old french muskets) and bayonets!