Did you find the software?

Don't know for sure.
But you can try contacting Qtronic in the netherlands, the do alot with sevcon
https ://en.q-tronic.nl

doubt you'll get it directly from sevcon, they do not offer a publc venue for this anymore.
there are several car conversion sites that sell the cable and encryption box with software though.
just google sevcon pcpak and they will be the top results like buggiesgonewild dot com, and some others.
They do explain to make sure what they sell is compatible with your controller so i guess some emailing between the seller and yourself to verify it's compatibility would be necessary.