It's not easy to find a complete long block. Let alone at a decent price.
You can find one in a car that someone might be parting out, as long as you get to it before half of the motor is picked over. You can check the junkyards, classifieds, etc. When I bought mine, I found someone who had actually bought a JDM motor from one of the yards that imports them and lost interest in doing a swap.
Thing was, at the time I was such a fucking DSM nubb, I really got fucked on the price. Not necessarily that the guy screwed me over (he didn't), but I just didn't know what to look for and I could have easily walked away with that motor for $300 less than what I payed for it.
If you're looking for a long block, then I'd try to do what I listed above. If you're looking to do a complete build, start with a bare block, and go from there. Personally, I could have saved a lot of money if I would have started from a bare block instead of a long block.
What are your plans? Complete rebuild or just a swap?