I use nav messages in the RINEX format. Here is a typical file.  If you don’t know how to get these files, feel free to use this shell script., which calls this script.

I also have some code that uses the SP3 format orbit file – but I have not distributed it yet. The main take home message is that you do not need precise orbits to do GPS reflections.  The SP3 files are just a convenience – you don’t need them (or GAMIT or GIPSY). Knowing how to run these high-end carrier phase softwares does nothing for you.