This is not a rule change, it has always been a requirement, but I think over time we maybe had not reinforced it with people new to the DE programme. We will be updating our DE information to include this.
As far as where to get a tow-hook, all cars came with them as part of the OEM tool kit, although I know many get lost when ownership is transferred. My suggestion would be either a Porsche Dealer (who can certainly get you one, but probably doesn’t have one in-stock) or, more likely one of our recommended DE inspection centres, who may have one lying around. Beyond that any of the Porsche Parts Recyclers will almost surely have some.