Chris, the Selza looks exactly like the one on my wrist at the mo only it's a non military Junghans, my strap is similar to the one on the unknown make (but obviously better quality :)) and dates to the 30s as far as I know. Apparently the buckle dates it if my info is correct.
As for the unknown make it's possibly a no name export post war Swiss watch. All watches are of interest, the Soviet ones I've seen have been small, around 30mm diameter and early post war, some were unmarked but I wouldn't call them poor quality compared to an every day Swiss watch.
Have you tried checking out the movement number?
Have a look at this site http://www.vintagewatchstraps.com/strapdetails.php He makes straps to order, mainly for the older trench type watch but also for later fixed lug watches like the one you show as well as the modern military watch. I've been very happy with all the straps I've bought from him.