The local CarMax may have auctions for the local "Mom & Pop" dealers - you won't be able to bid, but if you talked to a registered bidder ahead of time and told them what you are willing to pay (in cash) for a Leaf that day, they may bid on one for you. Point out that they won't have any lot insurance fees on it, since you'll be taking delivery immediately.
Yes that works pretty well. My wife wanted a specific model of used car several years ago so we told our regular mechanic (who has a dealer license) to find one in good condition at the local auction and bid up to a certain price. It was worth paying him for his time to attend the auction and filter out the cars with problems.
There are pretty massive subsidies on new Leafs now. $10k reduction by dealers as well as $7500 federal tax rebate (and potentially CA rebate if you are low income).
Manheim policy may vary across the world, but here in the UK they're open to private buyers on most lots.
My nearest auction house is Saltash, Plymouth and twice/weekly sales and upwards of 200 vehicles go through the books. It's quite something to see a car brought to the line, bid on and sold in 2 minutes.
Private buyers pay a larger commission per sale compared to bulk buyers, but hammer price is the same.
There's a twice-yearly plate change in the UK also, so in the coming weeks (from Sep 1) there will be a glut of used cars traded as part exchange for new vehicles.
Opening up the auction to private individuals doesn't bring more buyers, as the brokers are just middlemen -- all the cars they buy get passed on to end customers in a matter of weeks. It may bring more money, if people are willing to pay more to disintermediate the brokers.
However, this adds a lot of headache and risk for the auction operator - tons of uneducated customers who won't be able to pay, try to back out of bids, get pissed when the car has defects (auctions are typically as-is affairs), crowd the lot, etc.
However - if you see a car you want coming up, try asking a local broker to buy it for you for a flat fee, a few hundred bucks over the closing price. It's a guaranteed sale for them with no hassle ...
This is what I do. Friend of a friend is a dealer. He's at the auctions every other day. I just put in an order with him and he'll call me when he finds something good. I trust him. Having had a bad deal yet. Charges $400.