Are there real world examples of one way isolation between two populations?
You might want to look for asymmetric dispersal.
Asymmetric dispersal has been found in many freshwater fishes (such as bullhead; Junker 2012), freshwater mussel (Terui et al., 2014) and in marine kelp (bull kelp; Collins et al., 2010).
That being said asymmetric dispersal does not mean that dispersal goes exclusively one way. Maybe Blondel et al. (2020) reporting asymmetric isolation caused by waterfalls in guppies can be helpful to you.
I am also thinking of polyploid and invasive lines of sunflowers that often live along rivers and reproduce clonally through cutting, where cuts gets transported by the water stream. I co-authored a paper on the evolution of these invasive sunflower lines (Bock et al., 2018) so I should know the literature well but I don't and I am not able to cite a paper that really describes the dispersal and population structure of these sunflower lines. Such patterns might be found in Mimilus as well.
Planctons follow water streams and can therefore have very asymmetric dispersal too (Pringle and Franks, 2001).
I am also thinking of plants reproducing with seed flying in the air and living on a windy sea shore or in windy wide open plane (e.g. tumbleweed). But I cannot give you a reference.