recommend this one: http://www.dsflashcart.com/r4i-gold-3ds-wood-r4i-3ds-flashcard-for-ds-dsi-3ds-p-248.html they accept creditcard and ship uk. Just buy the r4i gold 3ds, working great on your 3ds V4.4.0-10
don't know any uk based site, but recommend a us based site here, nearly all the sites can send to uk, as far as i know normally do not need to pay the custom fee because they usually declare a low value to avoid the custom fee.
here is the guide for you Tutorial: How to update R4i gold 3ds card for 3DS V4.3.0-10 and DSi V1.44 here is one place to get a preflashed card: http://www.dsflashcart.com/ have checked game4deal, they are a wholesale site, you need to buy at least 10 cards everytime.
where? i didn't see it on the official site?
Ok, i found it , it's on the forum here: http://bbs.supercard.sc/forum.php?mod=attachment&aid=MTQ4MTZ8MTQ1NTY5ZWR8MTM0ODI3OTczNHw0OTJ8NDE0NDg%3D
if youu want the real time save and play gba games on your 3ds, you should choose DStwo, acekard 2i can not do that, if you only want to play ds games, ak2i is a good choose, another, i would like ak2i better than Dual Core.