This US vs. the rest of the world mentality HP seem to be locked into looks to have a workaround for us poor second-class UK TouchPad owners - pretend to be an American! Not in the physical literal sense, but actually by faking your country of origin in the TouchPad activation sequence. Yes, you'll have already set UK as your TouchPad country when you first set it up, but that can be changed afterwards via a rather convoluted route - all courtesy of a PreCentral forum posting. In case it gets pulled, I'll reproduce the steps here and at the end, you'll have a US-only app, Amazon's Kindle, installed on your UK TouchPad. Yes, it's very outrageous this hasn't had a UK release yet.
Firstly, you'll need to install Preware and also the Impostah application in the Preware catalogue. Next, run Impostah and tap the Activation option. Select United States as the country, English as the language, a fresh e-mail address (not one used in your original UK activation) and a password for the profile. Now tap on the Create New Profile button, accept the warning and it should create the new profile. Be warned that this will be your default profile unless you set it back later on (yes, I tell you how to do that as well).
Clicking on the small icon in the top left to go back to the Activation screen, you should be able to tap the "Login To Profile" button and - after accepting a warning dialogue again - you should be logged in as a "US user". It's now important to start the HP App catalogue application - because this is the first run by that user, it will prompt for the shopping country. You should pick "UNITED STATES" at this point of course. Immediately, you get the US version of the Pivot magazine, which is a nice bonus.
Leaving the HP App catalogue open, now run Impostah again, tap on "App Catalog" and in the field where it's asking for the geo.restricted.app.id, enter "com.palm.app.kindle" (without the double quotes). Tap on the "Get Application Info" button and then on the "Install Application" button. Voila, one freshly baked Amazon Kindle app on your UK TouchPad! When you first fire it up, it'll need an Amazon username/password to register the app - I used the one I have for Amazon UK without any issues.
It should be noted at this point that it'll be hard for you to install paid apps from the US catalogue, because I believe that requires a US credit card (this seems a ludicrous restriction to me - surely one of the benefits of a credit card is that it works in almost any country?). I haven't actually tried to purchase a US catalogue paid app myself - if anyone does manage it, please add a comment below.
I would recommend wandering around the US version of the HP App catalogue to find any goodies that are US-only (please comment on this post if you find any others, preferably along with the geo-restricted app ID for use in Impostah). Once you've finished doing that, you're going to want to set your TouchPad back to being a good second-class UK citizen again, so the next paragraph tells you how to do that.
Fire up Impostah yet again, tap on "Activation", set the country to United Kingdom, English as the language, use your original e-mail address when you first set up your UK profile and also the original password from your UK profile. Tap on the "Login To Profile", confirmed the warning dialogue box and your black tablet should be back to being a UK TouchPad again.