There are two easy ways. If you just want single cells, get them from Aircraft World
. Shipping is only $2.50. Takes about 5 days to get here.
Alternatively, search for a Dewalt DE9360 pack on ebay
. Last one I got was about £60. Can be as much as £80.
EDIT: It has just occured to me that you might be wanting the newer 1100 mah a123s. If that is the case, I think the only way at the moment is to get them from the US. As an alternative, a 2s pack of Saphion 1200s
would make a very nice Rx pack. Slightly higher capacity than a123 but only 2C charge rate. Discharge rate about the same.