in the materials room save a Material Collection and select all the materials you want in it (thats probably all materials for the item). That will be an .mc6 file and .png thumbnail in your material library.

 

You can convert an mc6 file to a mat pose file with a text editor if you have to but people need to get used to using mat files.

 

You will need to make a zip file with the mc6 and thumbnail and any image files you used for distribution.