Any ntc 3950 thermisistor will work. https://www.amazon.com/HICTOP-Thermistors-Sensor-Reprap-printer/dp/B0150YLX9C/ref=sr_1_1_sspa?crid=1BIA4QDCWAAO4&keywords=ender+3+thermistor&qid=1650318637&sprefix=Endee+3+th%2Caps%2C292&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFUMUNUQjhGUEJWQ0smZW5jcnlwdGVkSWQ9QTA2ODU3ODgyMjNLM1JBNVAyM0IyJmVuY3J5cHRlZEFkSWQ9QTA0NTAzNTVXRzZJNlRNSEVSNE4md2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

Here is a set of heater catridges and therms: https://www.amazon.com/Cartridge-Thermistor-Printer-Accessories-Eewolf/dp/B08HD3QLZP/ref=sr_1_16?crid=2QWD9ZCIGA7ZX&keywords=ender+3+heater+cartridge&qid=1650318900&sprefix=ender+3+heater%2Caps%2C202&sr=8-16

Here is the whole hotend assembly: https://www.amazon.com/Creality-Assembled-Extruder-Capricorn-Pneumatic/dp/B082PGCF2B/ref=sr_1_8?crid=2CT3PT9886GF1&keywords=ender+3+heater+hotend&qid=1650319075&sprefix=ender+3+heater+hotend%2Caps%2C196&sr=8-8

For the stock heater block, just make sure its not the canistor style thermisistor.

Any time you make changes to the hotend, you should do a PID tune afterwards to recalibrate it: https://www.google.com/search?q=pid+tune+ender+3&oq=pidtune+ender&aqs=chrome.1.69i57j0i13l4.7203j0j7&client=tablet-android-samsung-nf-rev1&sourceid=chrome-mobile&ie=UTF-8#