Was  momma   standing  by junior  when you found him?   Was she even in the  area?....   have you noticed her going back to sniff where  you picked the calf up?   

If  'no'  to  these.... you probably will not have  a  claimer...      With  a  good  pen,(escape proof...she  won't like it in there!)   at least a stanchion or    chute  with   removable  calf panel...  and   PATIENCE..  (I've needed  a week to 10 days  at times..   (don't forget to milk her off  at least once a day if  junior can't suck.)       Feed THAT milk to  junior... I swear  cows   can smell THEIR own milk... and  KNOW  which  calf   has been sucking them.

another trick is to throw  the  dog into the pen  with the pair.....  sometimes   momma  will   suddenly  want to be protective!... 
Once you hear her  'buzz' or  'humm'.. at the calf... you know you are on the  right path!