IRTPRO can do a Generalized Partial Credit model. If you are a student, IRTPRO has a free student version. Note that the student version is limited to 1,000 cases, 25 items, and 3 dimensions, and there is no tech support. http://www.ssicentral.com/irt/student.html

http://www.ssicentral.com/irt/student.html

MPlus and R

IRTpro

you may try the package 'pairwise' for the R statistical environment 

see: -->. https://cran.r-project.org/web/packages/pairwise/index.html

best

Jörg 

TAM is a new R module that can process the Partial Credit Model. I've used it for both unidimensional and multidimensional runs.

https://cran.r-project.org/web/packages/TAM/index.html

Thanks, David!