you can buy failure hash board s17+ or t17+ and scrap it.
but be careful that hash board Intact and most of heat sinks be on chip.
by this way you have more than 20 chip and other parts of hash board with lower price.
I don't recommend you buy a faulty or scrapped hash board to get the BM1397AG chip. Because most chips have been oxidized or damaged during use. Even if there are good chips, you need to clean and tin these chips before use, and some chips will still have unstable hash rate even after tin plating. After all these complicated and time-consuming operations, you're not necessarily going to get a good working chip. If the connection to the heat sink is poor, it will lead to poor heat dissipation and may even burn your entire hash board.