I have no particular knowledge of Cossack units active in the 'Order of Battle' of the Russian Imperial forces during the Crimean conflict, so you're on your own there. However, once you have a specific regiment or 'pulk' of identified, your first port of call might be Mark Conrad's translations of A.V. Viskovatov's seminal work (
http://marksrussianmilitaryhistory.info/Visk30.html) for English-language 'text only' descriptions. If you find a 4-digit reference to a 'plate' you wish to view, then fire-up your Google Translator Toolbar and head to the Russian-language Viskovatov 'original' (
http://listat.ru/T27/T27_sod.htm, and find the corresponding plate number. This will link to (typically) a 'sepia' toned copy of Viskovatov's illustrations, such as the example below:
Hope that helps.