Lots of places on the net sell engines. Most common are JDMHondaParts.com, HMotorsOnline.com, InlineFour.com, and JDMShit.com.

It should last forever as long as you take care of it like you would a regular engine and dont run the shit out of it. It's a Honda, it could possibly outlive you.

Most of the engines over the internet are out of cars from Japan. They aernt rebuilt but they usually average only around 25,000 miles. As long as you replace the timing belt and water pump to be on the safe side you should be just fine. You could always rebuild it with aftermarket pistons, etc. if you wanted.

But the B18 non-Vtec they are talking about I'm pretty sure is a US-only motor and you can usually find these at the same websites or in local import junkyards.