I've done that mission three times now and it seems to be triggered after you search some of the marked areas including information given to you by locals. Not sure how many areas you need to search, but what I'd recommend is that you just use a Humvee and start searching the closest position you get from the officer at the Elektozavodsk base (three red crosses marked on your map). Also search Vyshnoye and any towns on route to the positions given to; sometimes you'll see them in the process of getting attacked or there are locals who you can talk to for information.
My first two attempts I got the message but couldn't find Lopotev or Bardak, but on the last attempt I actually got Bardak and what an awesome scene it was. I don't want to spoil it for everyone, but it involved jacking a car and going on fairly lengthy chase.
From what I've read I don't think you can actually find Lopotev, but I may be wrong.
Cheers m8, but that's the problem - I've done all that. Spoke to both intel guys, got the background info from the Chedaki intel guy on Lopotev and Bardack, went to the three red crossed marked areas, found 3 parts of information/intel. Went to Novy Sobor and Vyshnoye as well as over to the East coast to Solnichniy, spoke to locals there who said to check the quarry. Went there and found one single enemy troop, killed him.
As I was travelling about the map between Novy Sobor and Vyshnoye, a message poped up saying I had captured Bardack, without lifting a finger. It just popped up and announced I had done that???.
South of Novy Sobor I went to the farmhouse that the locals tell you about and sure enough there is a farmer standing outside. But you run up to him and there is no way to enter any dialogue with him. Searched the castle up on the hill near there and found some intel/info.
Now I'm just running around or driving up in the hills at a complete loss as what to do next. There's always the "End mission" cheat I suppose.

It's almost as if some sort of "Mission trigger" that is meant to kick in, hasn't.