I will assume its a 1980 DR400 ST which is the Australian model and not the more enduro orientated USA spec model
so this is what i have come up with for DR400ST 64711-33000
that number doest show up on zedder, but i would have thought the axle would be the same as the SP400T.
if its the same as SP400T that means its common to 59 other model suzukis inc PE/TS/DS/RM
I find it hard to believe that the axle is only found on this one model so i have a feeling the part number i supplied above which is off a site that lists DR400ST (autralian spec) may be wrong