I started out using 3/4 inch hardwood flooring from sample boards which my wife had obtained from a flooring store that was going out of business. I used my table saw to rip them square and then used my mitre saw to cut them to length.
I had Brazilian Cherry, Bolivian Rosewood, Canary Wood, Hickory, Acacia wood, Santos Mahogany, Cumaru (Brazilian Teak), and many others.
I also got samples from Lumber Liquidators, Floor and Decor, and a couple of other flooring suppliers as well.
So all told, I probably have a couple of hundred blanks just from hardwood flooring samples.
Another source of material is to buy exotic hardwoods when they are on sale and rip them into blanks as well. I have been able to get Tulipwood, Kingwood, Paduak, Purpleheart, and Bubinga blanks that way.
Also, check with
https://www.diamondtropicalhardwoods.com/
You can buy 100 pen blanks for $25.00 and up.