How about contacting the theme developer? Seems he has not much interest in that theme anymore.
It is already listed as partly compatible so I guess it will need some work as the last test was quite a while ago (we lack resources to test 3rd party themes anyway). If you don't find a "comparable theme" on the themes section there most likely is none.
I would suggest you don't hold your breath.
The latest version dates from 2008, and if you look at the last comment on his page – which is 1.5 years old – there still is "lots of work" to make it work on 1.4.1. You could e-mail the author to see whether he works on it or he has abandoned the project.
As for substitutes, it depends on your taste. I would make two suggestions:
– m9 : simply modify margins in the style sheet and you'll get something similar to Mosaic. There were a couple of minor bugs when I tried it one year ago, so you will need to tweak it anyways.
- zpMasonry: his themes work and are almost always up to date. However, if you don't like the way it works (ex.: use of Flash), it's a bit hard to customize.
– zpAdroise: his themes work and are very up to date. I generally prefer Vincent Bourganel's interface over gjr's; however, Vincent's themes are updated at each version of Zenphoto, which might make customization a bit more tedious.
The last two themes make use of all possibilities of the current version of Zenphoto, which is good if you plan to add news, custom albums, comments, geolocation... in the future.