Lots of choices on eBay. Here's an example for "A" code key blanks.
https://www.ebay.com/itm/LOT-OF-2-19...1ZyoTS&vxp=mtr
Just be sure you order the correct coded blank for your locks. For example, my '69 keys are "E" code. I had the local True Value store cut mine. They refused to charge me anything, even though I'd offered to buy one of their blanks.
As stated above, I believe LocDoc also sells them.