Individuals who bought single CDs worth over 400k what brokerage did you use?

I just found out Charles Schwab website doesn't allow me to buy ​CDs value over 250k because that's the FDIC limit​​. I called told Charles Schwab​ thinking they could purchase a ​CD worth over 250k in their end. ​ I ​was told they can only buy ​one CD worth up to 250k per bank. I read on Reddit of people having CDs worth over 750k, 400k, 600k...how or where can I purchase CDs in that amounts?