well.... -10 is cold enough to warrant serious planning.
Any way you look at this, at some point you'll have to carry all this cold weather gear. Shopping as you go, thru the stans, is unlikely to provide much options, and shipping there is probably not simple. So I'd personally carry all that is needed, from the start. -10 means a down vest, 3-4 layers (i.e. you wear most of your tops), leggings, a warmer sleeping bag, a thicker sleeping pad, mitts, shoe covers, toque. I'd venture to say, 4kg/10L. Fairly insignificant.
OTOH, riding with a felt jacket purchased roadside, may be a priceless memory... Post pictures
