Leaving est implicit is common, especially in succinct sayings like this.
Punctuation works differently in different languages and classical Latin had almost none.
It is good to remember that all punctuation and capitalization in classical texts are due to much later editors, not the original authors.
Supplying a comma makes sense here.
To me the most natural completion is:
Ubi [est] ius[,] ibi [est] remedium.
Where there is justice, there is remedy.
To me the most natural translation of the implicit est in this context is "there is".
If it was something stronger like "exists", I would expect an explicit verb in the Latin original.
The construction ubi X ibi Y has many incarnations, such as ubi cor ibi patria.
Many recognize it and it is simple to use, so I find it an excellent method of expressing thoughts like this.
In English you can't idiomatically say "where justice, there remedy" without sounding like Tarzan, but in some other languages you can.
In addition to Latin, the same is possible (in the context of a motto or a poem) in Finnish, although we would normally add two copies of "is".
