Well, those are standard MX compatible switches. No big deal to find keycaps, but selection of numpad-only sets is more limited. Any idea what you want, style wise? Do you only want GMK or Signature Plastics or Drop, or are random sets and clones from Amazon/AliExpress okay?

Some of the higher end stuff will sell numpad only, generally for way less than the base kit (to wit...), but a really cheap set will cost the same for the full set, or even potentially a good bit less if you go bargain hunting and aren't picky.