After talking with a Walther rep who was visiting our local police equip store, I can shed a little light on this hi-cap mess.
First of all, Martini 13 is correct. IF it a .40, there were NO pre-ban mags made at all by anyone. If the guy says that if they are MecGar pre-bans, he's pulling your leg.
There are numerous mfg of mags out there in the world that produced unmarked post-ban 12rd mags for military contracts and non-USA markets. It is entirely possible that these were brought over privately. (Kinda like a grey-market car). MecGar would fit in this catagory. Say a private citizen in Germany bought a load of MecGars and shipped them over in his luggage, they would be unmarked and legal. (legal meaning IF he used them for his own use.)
If this citizen resold these mags, they would still be legal IF he was selling in very small numbers. A high number of resells would make him an importer and subject to Brady or require him to mark his mags LEO. (The Walther rep was unsure on the exact import numbers)
The Walther rep said that non-US Walthers do not have LEO markings on their high-caps and that MecGar does this for the US market only.
This entire senerio could also hold true for any weapon mag, anywhere, and we all know you can but almost anything on the net! A friend of mine just picked up some new Beretta high-caps that are Asian military surplus with zero markings.
So, getting back to where we started, it is possible the guy has hi-caps for sale. It is not possible that they are pre-ban.
(I wish I would have gotten the Walther rep's card to share with you, but all I remember is the name "Dennis")
"Clear as mud"