Here is the downloads page for the M3 DS Real:

FIRMWARE:

NEW: M3G6_DS_Real_v4.3g_E46_EuropeUSAMulti

old:

M3G6_DS_Real_v4.3f_E45_EuropeUSAMulti (old)

M3G6_DS_Real_v4.3e_E44_EuropeUSAMulti (old)

M3G6_DS_Real_v4.3d_E43_EuropeUSAMulti (old)

M3G6_DS_Real_v4.3c_E42_EuropeUSAMulti (old)

M3_DS_Real_v4.3a_E40_Europe USA Multi (old)

other firmwares:

M3_iSakuReal_v1.4

OTHER:

M3G6_DS_Real_Save_File_Converter_v1.00    

M3G6_DS_Real_Trim_Tool_v1.00