The short answer is that sorry, you are right, there is no tool for automatically translating SPSS script to R script. Even worse, such a tool would likely take several (many?) man-years to create, so don't hold your breath.
A small concession is that it is probably not to hard to create a tool for translating very small, specific subsets of SPSS to R. For example, if you have a chunk of code for reading in CSV files, then you could use regular expressions to extract the useful bits from the SPSS code and autogenerate some R code from them. In most instances however it will be far easier and faster to manually port the code yourself.
If all else fails, ask Bob Muenchen; he know a lot about porting SPSS to R.