If you don't have access to the dialer in the phone you'll need to get the IMEI from either the box the phone came in (usually printed on a sticker), any paperwork that came with your phone (some sellers print it on the invoice) or maybe even a sticker on the rear of the phone.
If the phone turns on and you can get to the dialer, enter *#06# and that should show the IMEI
These are customer to customer forums, you'll need to contact ID through live chat, Facebook or Twitter to retrieve details of devices they've sold you.