You are probably referring to the cast resin scales such as used by Gary (Traveller). Here's a link to some basic info on casting in resins of the various types: http://users.lmi.net/drewid/resin_faq.html#Anchor-44553

Each resin type has it's advantages and drawbacks... you pays your money and you takes your choice.

I think Gary offered to sell some scales a while back at a very reasonable price... If you are only looking for one or two, that would really be the way to go as otherwise you'll need to make rubberized molds etc. which all has their own challenges/learning curves.

Pen blanks and knife handle blanks are available from sources on the net as well... these would have to be cut to shape and sanded/polished to the desired finish.

Regards

Christian