Most of today's miners usually buy and sell ASIC miners through Ebay and Amazon. In the e-commerce market, these are the 2 largest e-commerce sites in the world, but the prices are very high.
Alternatively, you can also order an ASIC miner at the Bitmain homepage. The types of coin miners here are sold at a much cheaper price.
Despite being the 2 largest e-commerce sites, I still wouldn't trust the ASICs sold in them, just like those sold in Alibaba/AliExpress. They could be faulty or not what you expect.
In most official sites like Bitmain, the miners are already sold out.