In regards to miniature castings, this section covers mainly the 1700s and 1800s.

The main question is whether you intend to use 25mm-28mm or 15mm castings. The larger scale is good if you intend to play a skirmish set of rules or intend on using the popular ‘The Sword and the Flame’ set of rules. They are also easier to convert. Many companies make castings that can be used as is or converted. The companies of Old Glory, the Foundry, Minifig, Frontier, London War Room (old Houston) and Essex all make suitable castings in that range.

Many players prefer the smaller 15mm scales to either play tactical rules or even to play skirmish battles. In regards to the Turks, Battle Honors/Old Glory 15mm also owns the ‘Rank and File’ range. This enables them to offer Turks in both the 1700 and early 1800s era and allows the players to use Rank and File to fight the Crimean War and War of 1877 era. Minfig, and Alphacast (Greek) offer an 1800s line of Turks. Venexia (Italy) offer Turks for the early era. Russians for the 1700s and early 1800s are easily available from BattleHonors/ Old Glory, Essex, Minifig and others. It is only after the Crimean War when Russians become hard to find in 15mm. Rank and File makes Russians for the Crimean War and the War of 1877. Old Glory has released troops to be used in the Boxer Revolt and Russo-Japanese War. These are a little late for our era but the troops in soft cap and easily be used. Minifig has a Crimean War range.

In regards to Turkomans and other Central Asian troops, the Arabs, Indians, and Dervishes in turban can be used as these Moslems. Some of the Cossacks and Bashirs from various Napoleonic and Seven Years War ranges can be used as nomadic tribesmen. Even some Renaissance troops can be used as many warriors still carried bows and lances.

Russia's Manifest Destiny 19th Century Expansion

Introduction
Russian Campaigns During Their Southern and Eastward Expansion: Including Events of their Siberian Advance
Russia’s Oriental Gamble: Notes on the Push to the Pacific
Russia’s Taming of the East: Operations Against the Khanates of Central Asia
Chronology of the Russian Campaigns into Central Asia 1839-1884
Sources
Miniature Castings For the Various Russian Wars