Warning, links to Chinese retailers are rarely good for long. I update this link every time someone reports it being bad, but all you have to do is go to Aliexpress and search for "ender 3 all metal hot end" and make sure you get one with a 1.75mm throat diameter. If it's 4.1mm or it doesn't say, either ask or pick a different one.

Cheap all metal hot end at aliexpress - https://bit.ly/2QW1XCl