Perhaps someone will produce a retro disc of the month of first registration.
You can order a tax disc for any date from the Heritage Motor Museum:
Replica Tax Discs ~iw
Following a conversation over on
Pistonheads I ordered a replica disc from
this site on Tuesday and it arrived today. For £8 you get three discs with one inscribed with details if you wish. You can even specify what tax office you want on the rubber stamp. They are not perforated but they're a great deal cheaper than the "official" ones.

~iw