Hi,
I don’t think there is any ready-to-use answer, and I am afraid LBM-DEM is a task you will have to spend time on : the equations, parameters, and numerical resolution must be adapted to your very specific case, especially when resorting to external coupling.
Itasca specialists did address this issue in 2D (see Han and Cundall 2017) but I don’t think the code is distributed.
There might exist research codes on this subject, but again, I am not sure they are open-source
If you’re ready to dive into the subject, you can have a look on external coupling softwares (https://precice.org/). Notice that Itasca softwares support sockets through Fish and Python, which might be of help for dynamically exchanging data with external codes.
Good luck!