One thing I _wish_ I could do is get a stepped caps lock keycap to use on it like the one from the apple design keyboard, but that keyboard's 'caps are physically incompatible (I checked). In addition, getting the foreign models' modifier keycaps with the symbols instead of the words for the modifier action would be a dream come true. I always preferred the symbols over the words. The other problem is I tend to be picky about condition. I'd want a keyboard where the plastic is NOT all yellowed with age. That generally means new-old-stock which are HARD to find and when one does find them they're expensive. I'll report back on my findings.
Maybe you'd be interested in an International English keyboard (e.g. M3501Z)? I think all non-American keyboards have symbols instead of words on the keys. If you prefer the US layout, you could get a used non-US keyboard and swap the keycaps over (except Return, since the shapes differ).
If you can find a seller who's willing to pull the keycaps and send just those, shipping to the US would be pretty cheap, if you can't find one nearer.
Update: I just noticed an M0312 keyboard on the US eBay site
here. Currently $5 with one bid, ends March 29 15:57:40 PDT.
Update 2: Comparing the British English and International English key layouts, the only difference between the two is that the British English keyboard has £ instead of # on the 3 key. So if you had a British English keyboard, you could effectively convert it to the International English layout by replacing the 3 key with one taken from a US English keyboard. (I mention that because if you decide to get hold of a non-US keyboard for its symbolic key caps, a British English one is likely to be easier to find than an International English one.)
There is an article on the Apple web site with links to diagrams of the various types of keyboard layout:
http://docs.info.apple.com/article.html?artnum=304933. Note that, since the article really refers to newer Mac keyboards, there may be some slight differences between the layout picture and the corresponding Extended Keyboard (II). Specifically, the
International English layout picture shows the text on the Control keys as "ctrl", whereas a real International English Extended Keyboard II (M3501Z) has "control" on those keys.