Have you heard of <a href="http://www.bricklink.com/index.asp">BrickLink</a>?

It's a simple marketplace where you can buy/sell/search for that one LEGO piece you're missing. We spent hours playing around on the site and I'm pretty sure they have everything. And if they don't, you can always place a Wanted ad.

This should save you quite a few headaches and bundle of cash as you take your LEGO skills to the next level. I mean, as your kids take their skills...oh, you know what I mean!