The most likely reality is that your best bet, for a 10l size, would have been to buy one when in Koln; finding these stateside is going to be dependent on someone else having done the same.
Your other alternative is hoping to find an international ebay seller who has one and is willing to ship to the USA.
On top of this, the tapping hole on the older variety of these kegs require special "plugs" which are a one-time use item and only available to the USA from a few retailers. Additionally you will need a specialty tool to install the plug; you will need to again get lucky on a foreign ebay seller shipping to you to get one at a fair price, shell out huge money to the one vendor who sells them, or fabricate something of your own.
This style of keg is also referred to a bayrischer anstich or bayrischen anstich.
Needless to say I have done lots of research into this style of serving from a keg myself, and even tried to acquire some kegs from from Germany only to have something (different things on multiple occassions) occur that prevented them from reaching me stateside.
So I salute the idea, but at least in my experience, it may be prove to be extremely difficult to execute (and cost a fair investment most likely too).
That said, if you find a good source for the 10l size (or heck even the 20l size) please do share!
Yea, you're right that I should have bought one when I was there. You can get a full 10L of Kölsch for €50 (including the keg deposit).
I thought about trying to get someone in Germany to send an empty one here, but I have a feeling that the hassle and cost will be prohibitive. I thought you could have a reusable plug (and/or the brass style tap didn't need one of those throw away plugs), but I could be wrong.
I hadn't come across the bayrischer anstich name before, but I'll use that to aid my search, thanks.
I do have a source for the kegs in the US. Schäfer containers has a US location, but they quoted me at $212 for a 10L. I've seen places selling 40L Firkins for $108, so I couldn't justify the price. I don't know who's buying 10L pittermännchens for $212, but it seems crazy. Another place, BLEFA, quoted me at $285 for the 10L and $375 for the 20L. Ridiculous.
My next tactic, which I'm doing now, is to contact importers/distributors who bring in Kölsch and see if they'd be willing/able to get a pittermännchen for me. Other than paying hundreds for a tiny keg, I may have to wait until my next trip to Germany.