One of my many hobbies is model railroading. I focused my model trains on European trains in HO gauge. I belong to European Train Enthusiasts (
www.ete.org) that is dedicated to European model railroading. While I run HO gauge many of the club members run z-gauge.
Marklin and Porsche have a history of producing Porsche related railroad items. In most cases the items are very limited production and in some cases, such as with the z gauge start set you saw, are available only at the Porsche Museum store. If your lucky enough to be there and see something, grab it. Production is often limited to a 1000 or so items. Once their gone, your best bet is likely to be e-Bay. Because of their rarity and high demand, they command a premium price on e-Bay.
I have a couple of Porsche related items in my collection and one of these days I'll post some photos.
One other thought with regards to price, Marklin like anything else manufactured in Europe is becoming more expensive do to the deteriorating exchange rate. Since I don't run z gauge, I don't track the prices that closely,but HO start sets run anywhere from a few hundred dollars to $2400 for a full digital 2 train start set.
Good luck with your search
