Can you clarify a litte please; why is it so important that they come from the same store? If we understand why it might be easier for us to help.
At a guess you're probably trying to dodge Europe's crazy high prices while incurring only one set of currrency conversion and import charges but think about it; if the DS it has a dead pixel, some other defect out-of the-box or develops a fault within 1 year you're going to want to exchange it.
Seriously, stick with getting hardware from somewhere reputable with a good warranty scheme. I know there's some very respectable flashcart sellers out there, but can you really guarantee they'll still be open a year from now?
That out of the way, if you're still looking to import a DS PlayAsia is probably your best bet.