For knife-making and other DIY projects, I've bought a lot of steel from Online Metals:
https://www.onlinemetals.com/?gad_source=1&gad_campaignid=6502026653&gclid=EAIaIQobChMIhIzn_afWkAMVxR-tBh3SYwLcEAAYASAAEgIPGPD_BwE
You can sort by size, shape, alloy etc... they usually have what I need...