You may list Products.PFGSelectionStringField to buildout.cfg or setup.py in your own package.
Use zc.buildout and the plone.recipe.zope2instance recipe by adding Products.PFGSelectionStringField to the list of egg:
[buildout]
...
eggs =
...
Products.PFGSelectionStringField
You may also list to install_requires to setup.py within your package.