IMHO neither side needed a BUK.
Kiev had nothing to shoot at, by a BUK.
Russia never bombed Ukraine from air.
Separatists had nothing in air at all. No "aviation" :o)
What to shoot at? Birds?
Separatists didn't need a Buk either. They have shot 24 Ukrainian airplanes very successfully, before the Boeing tragedy, having no BUKs.
By "conventional" arms , in their disposal. In the range - from fighter jets to large transport airplanes, carrying Ukrainian military personnel.
What for would separatists need a BUK?
BUK, as I understood it, fires at high altitudes, 10,000 metres, exactly where passenger aviation flies.
Ukrainian military planes flew 5,000-7,000 metres, within the range of the existing separatist arms. Proven by the loss of it all.
Who, in his right mind, would take aim at 10,000 metres where there is, technically, nothing military above Ukraine?
Whoever (if it were a BUK from the ground) took the aim high up there - what was in mind? To find there - what? on earth