on the source server, run the following script to find out where your back files are:
select database_name,backup_start_date,physical_device_name
from msdb.dbo.backupset bs
inner join
msdb.dbo.backupmediafamily bmf
on bs.media_set_id = bmf.media_set_id
where database_name = <your db name>
order by backup_start_date desc