This is impossible. These three cities are inaccessible.

I have, however, gotten items that have said "Worth [x] in Saint-Denis." So either there is a way, or there will be sometime in a future update. 

I noticed that as well... I haven't seen any items worth anything in the other 2 destinations but I suspect Saint-Denis might be accessible somehow.

The Balkan Dagger was valuable in Merv during one of my play throughs.

Well,in Steam guide map(it shows all the routes anyone can take,all of them)and there are only six cities that are not reachable:these three,Las Vegas,Duluth and Winisk.So these are not reachable.Here is the link:steamcommunity.com/sharedfiles/displayimageformodaldialog/?imageurl=http://images.akamai.steamusercontent.com/ugc/648877624321805784/592F1FB9A14E19429C96184F1894C2CE8861B6DE/

Well,I don't know about Lusaka,but the destination's change is a part of an adventure usually.If the route from Krasnovodsk was not going for Herat but for Merv,then the adventure with the walker from Herat to Waltair would not be possible.And if the submarine was not going to be kidnapped and go to Batavia or Colombo but was going for Saint Denis,then the adventure with Captain Nemo could not excist.And the worth x in Saint Denis or Merv is just a trick for trying to go there.