The DLCs of ME1 are free, they are included in the current downloadable versions on Steam and on Origin.
If you have an old Steam installation you can find them here, (I suppose that is the side you already found, but the ME1 DLC will not be in your Library regardless of the client you use.)
If you open the ME2 section of the page linked above you will see two sections, the DLCs under "Cerberus Network Downloads" are free to use.
The DLCs under "DLC" are not free and must be purchased. (Link) (They also wouldn't be in your Game Library but in the "Extra Content" section in Origin.)
Edit: Typo
