"this is why I just love to see buy-ins, which we never saw until the concentrated effort to constrain the shares available to lend as much as possible (e.g., by posting anti-short high-ask orders for shares held long in non-registered accounts)."

While there are might be some merits to this, I think it is a common misconception and does not really affect ability of the brokers to locate lenders of the shares. The broker's customers (eg. retail investors like us) is just one source for those shares. Also, I was told that most of the brokers don't bother with small borrow orders for the stocks like PTK (which are considerd "low quality" stocks from a broker's perspective) so it must be a big customer willing to borrow a large lot.