Great to hear from you Bill! The weight of the paper is not that important so you can use 67 lb. as well. In this case 'Vellum' is a type of finish and not a type of paper. There is translucent Vellum which is a type of paper and I use it as a bearing surface for moving parts that contact each other.
Lately I have been using XEROX 67# Vellum Cover. It can be purchased at Office-Depot and can be found online for sure. The Vellum surface has valleys and crevices that will hold larger amounts of colored pencil for a given area which is just what we want. Just noticed that the paper listed online is Ivory colored and not white, which is not good. Hopefully the store will have the white, I'm sure I purchased it there. Otherwise you will have to search elsewhere.
The fun thing about mixing and coloring like this is that it brings out the artist in us and it is challenging and fun too!
The glass file that you have appears to be fine. I'll get one like yours and try it. We cannot have too many tools!
The following links have information on paper surfaces including the Vellum finish that we have been referring to.
Paper Finishes Demystified for Specialty Paper from The Paper Mill Store
eBay Guides - Paper Weights and Finishes
Here is a link with vellum finish papers.
The Paper Mill Store .com
When you get the color mix right but it is not dark or light enough, just add white or black in very small amounts rather than adding any other color.
This does take some practice but is worth it.
Good luck and enjoy!
Denny