Is there a library available for the LSM303D that can access the LSM303D via its I2C interface, using one of the “SoftI2C” libraries, so I can access it via my Arduino’s non-I2C Pins?
There are several collections of software I2C routines for AVR processors. Google will be happy to show you where they are. Try including “bit bang” in the search terms.
You don’t need a library. It just takes a few lines of code, calling the I2C routines, to read and write the registers. Your time is much better spent understanding the data sheet and writing those few lines, than modifying someone else’s code.
Finally, it might be easier to use the I2C hardware pins for this, and change whatever else needs to be changed to free them up, than incorporate bit-bang code.