You know, if the past few packs are any indication, I'd suggest you do what I do: Find a good friend, maybe 2, and do it with them. Enough achievements in the last pack only required two people to do, that me and one good friend sat in a private server, farmed for 40 minutes, and voila, we both had all the weapons.
And no, I'd hardly call farming cheating, not by a longshot. Cheating is these guys who unlock the weapons through console commands and then Valve lays down the hammer on them. If Valve wanted un-farmable achievements, it'd be easy with a couple requirements:
All achievements must accomplished on Valve created maps.
All achievements must be accomplished in servers with at least XX people.
That would make it a much bigger pain to farm, but even then, it'd still be totally doable. If you consider farming a problem and cheating, better live with it, 'cause there's no solution. Just focus your efforts on keeping farmers off live eGO servers.