Mouser, Digi-Key, fleabay.
We got away from the "baggie" parts when suppliers selling original-numbered parts appeared in the '80s. Had a local parts dealer who would reverse-cross from a NTE/ECG number to an original OEM "2S" part number. His prices were better. But that outfit dried up and blew away with the rest of them years ago.
We got serious deals on parts from 'secondary market' guys like All Electronics, but they closed earlier this year. These guys launched a similar operation, but their product line is a bit narrower
https://aretronics.com/
Can't forget Marlin P Jones Associates in Florida
https://www.mpja.com/
Linear and radio-final transistors can be had from ICA manufacturing/FatBoy.
https://www.icamanufacturing.com/
Yes, they have a lot of other stuff, too.
But those are the highlights. As always, subject to change, just like the rest of the universe.
73