Not even sure which Gimp version you are now using, however since I made some screenshots you are getting them.
A little bit of investigation. All this using a Win7 64bit VM and a Partha Gimp 2.8.14 pulled from the Internet Archive.
First the NIK collection.
The Partha Gimp 2.8.14 did not have the required python plugins installed. Maybe there is a later 2.8.x version, I do not know. If this entry is missing, then update to a version that has it.
Next gmic-gimp plugin.
The latest QT version failed in Partha Gmp 2.8.14 on a dependency, libidn-11.dll Probably easy to fix, if you are keen. An easier way is use the gmic-gimp GTK version.
Get the zipped version, unzip, put it somewhere convenient, add it to the Gimp folders path
Does it work, Yes it works. Remember to update the filters, 491 here. Using film emulation, it does pull the required file from internet as required. They are not pre-installed unless you do that yourself.
Where are the gmic files held in Windows …\Users…\AppData\Roaming\gmic
hope this helps.