I've lost my Disclosure
Unfortunately there is little that can be done.
The CRB will re-issue a Disclosure only if the original was lost in the post en-route to you and it is reported within 60 days of the issue date. (Difficult if you didn't know it was sent)
In truth, for most people the Applicant Copy (that you get) is only to let you know what was on the Registered Body copy which the employer sees and which is regarded as the "master".
Any employment decision will be based on the RB copy, as this may (very rarely) contain information that cannot (by law) be revealed to the subject relating to current investigations or policing methods that may be devalued if they became general knowledge.
With the CRB no longer endorsing the practice of organisations accepting Disclosures obtained for other roles it is likely that any organisation wanting to see a Disclosure will ask you to get another one anyway.