if I understand your question right, you already have a number of materials.
Then there is two options i can come up with to reuse these in other parts.
1) create the new palette as John describes when you have a "rendered part" on screen, then open the "materals in part" tab, then copy from this palette to your new palette. ( i know, one can only copy one material at a time...)
2) The other proposed uses an old and maybe no longer supported method. ( Still works though)
RMB on each of your materials in in the "materials in part", - Information. The text that shows up in the listing window is the same as the contents of a ".lwk" file.
Each material you select then might have two sections in the listing window, one referring to "Begin material" and one section "Begin texture", in modern versions of NX these two is the same as "a material".
You can then either save each report as a single material, but you can also copy paste all these reports into a single .lwk-file.
When you want to use it, go View-Visualization- High Quality image, then in this dialog there is a "Import from LWK file".
You will need to add all materials and all textures in a subsequent dialog.
Regards,
Tomas