I guess you're talking about foreign garbage coming in from abroad, and those eliminated circuit boards have the MCU and chips you want.
Go to Longtang, Qingyuan, Guangdong, the largest electronic foreign garbage disposal plant in China, and see if you can find it. But they are basically sold by tons, so it is difficult for you to get a single piece.
Moreover, if you think that chips and circuit boards have been used four or five years since they were eliminated, PIC 18F2550 has a long service life, so it is difficult to find PIC 18 circuit boards now.
Also, although disassembling the chip is cheap, it can't guarantee the quality. I suggest you spend money to buy an IC.