You do know Thomas that Kolchak's Cossacks were indistinguishable from normal Russian Cavalry?
(At least in 15mm scale -- technically they should have nagaika whips and slightly baggier trousers, but you're not likely to spot that.)
The "Cossack" dress with fancy kaftan is not traditional Cossack dress at all. It is the traditional dress of the Caucasian Mountain peoples (Chechens, Ingush etc) and was only worn by them and the two Cossack hosts that neighboured them -- the Kuban and Terek.
Orenburg, Urals and Siberian Cossacks fought with Kolchak (though not in large numbers, actually, as they mainly fought for their own Host Armies). They would never wear the Caucasian kit.
What you need is the PP regular WWI Russian cavalry of WWI. Packs 42, 43 and 44 (they were half lancer). Swap some heads to fur cap perhaps.
(BTW, I second Alan that the FOW Cossacks are totally unsuitable even as Kuban or Terek Cossacks for 1919-1920).
adds an infantry platoon to his WWI Brits.
