Hiya
Search out a few electrical wholesalers as they'll stock allsorts of adapters and connectors etc. I picked up 4 UK to USA adapaters for the bits and pieces of electronics I usually buy on my trips over there. I think I paid something like 99p +VAT each for em. The place I know is over here in the Slough trading estate. There's probably many more around London, so maybe hunt around the area you'll live in to see if they can get you some.
Here's the TLC website (dunno if they actually list em, but they're in their printed catalogue of course)
http://www.tlc-direct.co.uk/Main_Index/index.html?utm_source=overture&OVRAW=tlc%20electricals&OVKEY=tlc%20electrical&OVMTC=standard As for Radio Shack - yep they used to be in the UK, always under the name 'Tandy' wayyy wayy back in the day. Then they did all get rebranded as Radio Shack, just like the US stores. From vague memory, Radio Shack disappeared from the high street in the UK around 4-5 years ago. I don't know if they were bought out or simply just pulled out of the UK market. However, theres quite a few homegrown UK electronics outlets that are like RadioShack, Comet is one, Currys and Dixons also don't forget Argos as they carry lots of lines of items. They probably will carry the adaptor you mention.
HTH!
Dennis! West London & Slough UK!!