What is the legal issue that you're dealing with? Trying to get around a state limit of greater than 10-round mags by using pre-ban mags? If so, you're probably going to have to get them from someone IN-STATE, with some form of documentation.
Just because a seller tells you they're pre-Ban may not help you if you've got to prove it, later.
At different times I've had a bunch of CZ and Tanfoglio pre-bans, and they simply were no different than post-ban mags. (Some came with new guns, as CZ had a big inventory of pre-bans that were able to sell with their 75bs. A lot of shady dealers and distributors swapped some of them out on the guns, inserting 10-round mags and selling the 15 round mags at a premium.)
I'm not sure the 5 extra rounds are worth the money. In a self-defense situation you're unlikely to need that many rounds, and at the range, the extra capacity is convenient but not important. Just get several good quality 10-rounders.