Sources for LiFePo4 cells / packs (A123 / K2 etc)

Having found a couple of nearly-there packs listed on Hobbyking in their LiFePo4 section I'm after any other good source for LiFePo4 (or A123 / K2 cell packs) in 4S1P or 4S2P (I could join 2x the former together if needs be). It seems they were easily available 1-2 years ago but have become harder to get hold of.

Does anybody know of a good source for these? I'm not adverse to putting together a pack from cells given it may be the only choice, just if I can find somewhere decent that provides them!

I have some new packs of a123 but they were put together in in single 10 cells so 37v, easily changed though. Got around 3packs, so 30cells available.