Wir haben diese leider nur noch in Größe 36.
is translated as
Unfortunately, we only have this one left, in size 36.
In other words: "We only have this ONE; it is size 36.
But wouldn't the German sentence be more precisely translated as "Unfortunately, we only have these/this in size 36"? It's a small distinction, but this implies there might be several blouses left, but they're all size 36, instead of we only have ONE blouse left (which happens to be size 36).