Right now that code is only in a private repo and is based on the C++ version of ITensor. If it’s important for you to try I could find out more and possibly get you a copy of the code.
The good news is we are eventually going to have support for this same method through a more general effort (in the Julia language) to support DMRG and TDVP on arbitrary trees, which would include fork states. I’m not sure when that will be ready, but there’s been a lot of progress on it already so maybe within the next 6-8 months?