Some DOD distributors use to have replacement battery covers.
from what i hear none of them carry them anymore...because the manufacture went out of business.
No not DOD or Digitech a separate company that made battery doors...
Calling a DOD distributor or DOD tech support might be your best bet....maybe very old dealers might have some laying around use the DOD Locator
....or find the links at the Website
i think the Grunge pedal and the old yellow FX50B overdrives go the cheapest on Ebay.basically you buy another pedal to steal the battery door
Sometimes you get lucky and see battery doors on ebay...they will sell as high as 5 to $10
finding a grunge or fx50 for $15 is sometimes the cheapest way to go if you don't want to wait.
i searched the bay and found these...always a DOD on the bay FX50B Grunge
with shipping cost it might be better to buy a used pedal at a local music store...since shipping can be around 6 to 7 bucks.
sorry man wish i had the magic answer...but the company that made the replacements went bye bye many years ago. I forget the name and it doesn't matter now anyways..and DOD for some reason refuses to sell them direct....maybe they smartened up......otherwise a smaller distributor where you can actually get a human on the phone is the best bet.