The CDS examination roll number is issued few weeks prior to the scheduled date of the CDS exam, CDS admit card is also made available the same time. The roll number is never sent on the e-mail ids. So candidate must not miss their roll number in any way.
CDS account Number
Now in case if you have missed it, the only way you can get it is by downloading Provisional Admit Card. Candidates will require to check whether the provisional admit cards are available or not by visiting the UPSC official website. You can download the provisional admin card by providing the registration number and date of birth.
There are also chances you do not get the dates and admit card, if it is so, then you have lost your chances. There are various forums available where you can request to the UPSC officials, requesting them to re issue another admit card. Do not forget to mention personal details like candidate name, registration number and date of birth.