I believe this is what you're looking for:
http://www.ebay.com/itm/151071023024
That fellow has been offering these for a while, so he must have a number of them.
Note the modifier row -- 1x modifiers and 6x space bar. These may not fit your layout. Also note that these are MY switches, so the location of the switches is different for some keys (I'm not sure which - perhaps the shift keys.) And the MX stabilizers may not fit the MY caps.
That said, it is certainly cheap: $15 + $9 shipping in the US. The seller does not list UK shipping, but you can ask. If not, let me know if you need a proxy.
Here are some more sellers of the same keyboard; the first one offers UK shipping, but it appears to be high.
http://www.ebay.com/itm/200824157908
http://www.ebay.com/itm/350572017058
http://www.ebay.com/itm/230592242239
Here is a keyboard which might interest you:
http://www.ebay.com/itm/271285517855
White on black double-shots -- a more common modifier row layout -- MX switches so you can use all the keys and stabilizers. I don't know what type of MX switches it will have -- the wiki says HR is black or clear, but my HU board has browns, so the wiki is not always correct.
It might be a bit expensive for just harvesting keycaps, but you can harvest the stabilizers and switches too. Otherwise, watch for G80-8113HRxxx boards at a lower price -- I bought a couple for about $40 last spring.
