Made your own, or used another provider?
An unenrolled deed poll isn’t registered anywhere, so there’s no official copy to request. Another provider may still hold your details, but it can’t give you back a signed original.
If you changed your name recently, the simplest fix is a new deed poll, signed in your old and new names in front of two witnesses and dated the day you sign it. It does the same job as the one you lost for every organisation you haven’t updated yet.
Never backdate it. A deed poll must show the date it was really signed, and HM Passport Office checks that a deed poll is dated and was made at the time of the change. HM Passport Office: evidence to change a name