I have never seen anything that has more desirable bokeh than the Vivitar Series 1 90mm "Bokina".
I have seen several lenses that come close. The latest one that really impressed me was the Vivitar 85mm f/1.4 (made by Samyang) that sells for under $350 new.
It was a well-built solid feeling manual focus lens with "A" contacts.
Very similar focal range to the Bokina, a little "faster", and a lot easier to find than the "Bokina"... but I wouldn't call it a Bokina replacement.
I have never used the Pentacon 135mm but I can say that I don't really care for that focal range on a APS-C DSLR camera.