Portriga has been off the market for at least a decade and it was one of those papers that, unless frozen, didn't hold up well. The base usually fogged/turned gray, and the contrast range died. It was even finicky when it was fresh, with emulsion problems occurring quite a lot. It was great paper, and there isn't really anything like it out there. If you ever did find this teacher, I'd test it before putting down even $.01 because of how it deteriorates quickly over time. BTW, it was discontinued because it had Cadnium in it, and environmental regulations forced Agfa, and ultimately all producers of warm tone to change their formula. Most did, some didn't, like Kodak with its Ektalure paper. That paper actually holds up rather well over time and I still have about 500 sheets of 16x20 that is around 8 years old.
As for Bergger, they actually had to change companies that produced the paper for them and in doing so changed the formula some. It is in limited but growing distribution now, with most if not all the line once again on the shelves, or on its way. If I remember correctly, John, the US distributor, told me that by the end of May the complete line in all sizes and surfaces should be done. But to be sure, contact them through their site.
Hope that helps.