As Steve has indicated the UUID can give you this. Here is a link to one website that can generate either the Version 1 or Version 4 codes. Like any random sequence, the level of randomness and security depend on the key that was used to create the series. So the achieve true random "selection without replacement" requires an infinitely large volume of codes.
https://www.uuidgenerator.net/The UUID comes close to this for strings of numbers. If you need alphabetic characters you could simply try using hexadecimal numbers or invent a high base.
Finally, you do not say how random the sequence needs to be. Often, non-duplicated sequences have no need to be truly random, so selection 1 is AAAAA then selection 2 is AAAAB, followed by AAAAC, etc. Keeping track of which codes have been created is easier and if the string of digits is long enough one may never know if the value is the last in the series. So a counterfeiter attempting AAABA would generate an out-of-sequence value which would be invalid.
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Danny Rich
Senior Color Physicist
Sun Chemical Corporation
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Original Message:
Sent: 07-13-2017 01:58 PM
From: Bill Fechner
Subject: Software for random number generation
Has anyone used a software that can generate random 12 character alpha/numeric strings as needed based
on a rule that prohibits duplicates? Thanks for your time!
Bill Fechner, CEO
The Advertisers Printing Company
1229 South Vandeventer Avenue
Saint Louis, Missouri 63110
email: <maskemail>wf@...</maskemail>
direct line: 314-652-9924