Nearly anything can be made into pen blanks. Here are some suggestions:
Boards:
Instead of buying expensive pen blanks, buy the ends of the nice big boards in the back of that San Diego Rockler Store. My local Rockler will cut off the end of a board as long as you leave a minimum of 4 feet of board left for them to sell. You can buy a 6 or 12 inch end of a board and cut it into pen blanks for much lower cost than buying individual pen blanks in the pen blank section. Use a bandsaw or other thin kerf blade to reduce waste when you cut up the blanks.
Old Furniture:
I made pens from my parents' old china cabinet. They had given the dining room set to the neighbor. When she moved out, all that was left was the base, and she put that out on the street. I salvaged it and used some of the smaller scraps to make pens for my family, who appreciated the sentimental value. You can find nice hardwood furniture at the local thrift store and many free sources.
Old Corian Countertop Samples:
See if your local kitchen supply has Corian samples to give away. Make them into pens.
Downed and Trimmed Tree Branches:
Woods that have little value as furniture can be spectacular as pens. We had a high wind a few days ago, and a small branch of our pepper tree came down. I turned a small piece, and it was very pretty. I saved some bigger pieces and will make a few pens from it. If I can salvage a big enough piece, I may try making a pepper grinder, which seems fitting. Remember to give your fresh wood blanks plenty of time to dry before using them. Protect the ends with wax or something similar. I am eager to try a piece of our bottlebrush tree when we trim it.
Friends, other giveaways:
A friend gave me pieces from the cherry tree he had to remove. A nearby city removed their olive trees and everyone got a windfall from that. Any time you hear one of those loud chippers, go over and see what kind of tree they are chopping up. If it is a nice hardwood, ask if you can keep a few branches. They won't mind. Usually the problem is too much wood, not enough time.
Get Creative:
You can make pens from nearly anything. Wood is everywhere, and you would be surprised at how pretty random scraps can be when turned into a finished pen.
Even bland, grainless wood makes nice pens. One of my favorite pens is a cheap gold Slimline made from plain maple. It doesn't have the drama of the pens that people post here, but it has the right shape, feels good in the hand, and writes well. It is a simple wooden pen that is vastly superior to any cheap crappy plastic pen that people use these days.