VPN won't matter, OneWorld Explorer tickets are all priced based on the point of origin for the base fare, then the taxes and fees vary wildly by which airports and airlines you put on the ticket. In the Europe area it's CAI and OSL, and in Asia it's ex-Japan.

For ex-CAI I think the only one that still works on with the online tool is if your first flight in on RJ but that seems to get ticketed by QF, which is something you don't want. AT might work as well, but that also appears to get ticketed by QF via the online tool. Apparently AA is issuing them still but has to be on the phone and then you have to play by their rules (any AA flights have to have AA flight numbers, some partner flights aren't bookable, etc.). Ex-OSL however should be ticketable by anyone.

FWIW if you're keen to position for it, ex-TYO has much lower YR/YQ fees typically so while the base may appear higher, in reality it's all about the same. In the pricing thread you can get some ideas what people's recent prices have been. There are some ex-CAI, OSL, and TYO posted in there, OSL and CAI tend to get some ridiculous YQ/YR fees, seeking out a travel agent that can plate on QR via Sabre seems to be a way to avoid much of them, but so far no one has posted that they've made the effort to do so.