ECU replacement

I assume you are referring to the ECM or the Engine Control Module. If so then I attached the OEM part number. You can do an internet search for that part number and see if there is one available. I did a quick search and found that most places that carried them are out of stock due to it being discontinued.

Any time there is a discontinued part we need to relay on the aftermarket or a refurbish company. If you simply do an internet search for "2002 Mercury Villager ECM" then you will find companies that will refurbish your ECM or send you one that is refurbished and will want you to send yours so they can fix it and sell it to someone else.

Unfortunately there is no easy way. It is just going to take some searching online. The only precaution I will give is make sure they have a return policy if the "new" ECM has an issue.

Here is a pretty common website. I am not endorsing them but I know people that have used them and had pretty good success.

https://www.fs1inc.com/mercury-pcm-ecm-ecu-engine-computer.html?make=85&gclid=EAIaIQobChMI1oe_rKvC5wIVw56zCh3yHQmwEAAYASAAEgJXXPD_BwE

You need to know the exact part number you have in your vehicle. Then use that to look online for one. Rock Auto shows they have one of the possible numbers but not the other. You can also get a used one from a salvage yard. In both cases it will need to be programmed to match your vehicle.