Where can I get download links for the Mass Effect DLC?

Here's Bring Down the Sky:

http://lvlt.bioware.cdn.ea.com/bioware/u/f/eagames/bioware/masseffect/dlc/MassEffect_BDtS_EFIGS.exe

The other one is harder.  Since you've paid for it, it will depend on who you bought it from.  If Origin, it should be in your Origin library.  If Steam... I don't know.  If other, I'm not sure.  It will depend on the store.  I'm told it's terrible, so I wouldn't knock yourself out over it.