Whilst it may sound an easy thing to do, have a master list somwehere. Geting someone to take full responsibility for operating it is another thing, Im lead to believe if someone did run such a scheme we could use their advise as a legal issue to support cases were obselete kit was in use. AKA "we continued used x kit from y supplier because there was no obselete notice on the master list.
What we do is what Brian suggests above. We run a list annually of all models in use. We check the list from last year and any that dont have an obselete date on them we contact the oem and ask the question again.
Its a bit of a bind 1st / 2nd time around but the list should get smaller as time goes by.
If you cant decide on questions just use the PPQ section.