If there is a chance someone else downloaded them, they may be on your server in the HIPAA folder. Look there to verify if files are there.
If no one else could have downloaded them, then contact Palmetto GBA (Technology Support Center) at 1-866-749-4301. (You will need your submitter ID, NPI number, your Tax ID number and your PTAN. The Provider Transaction Access Number is your provider number. Barnestorm does not store this info. for you.) Ask Medicare to restore an ERA(s) for download. Give them the "timeframe" of the ERAs that's missing. This will put those ERAs back in your mailbox for that specified period of time. ERA(s) should be available within 24 hours.
Here is a link to the PGBA web site for more information:
http://www.palmettogba.com/palmetto/providers.nsf/DocsCatHome/Regional%20Home%20Health%20Hospice%20Intermediary%20(RHHI)
Copy and paste the link into your browser if clicking it doesn't work.