So forget the third-party sites and hit up the people you know will be interested. You could tailor Kickstarter-type reward levels (e.g., pay $X now and get a complete playset of the cards when they are printed) for the existing players and see what funding you can get via that means.
My understanding though is that if you go through Kickstarter/Indiegogo that when people commit to something that the funds are automatically locked away to be used if the project is fully funded.
If we tried to do something like that here on the forum, there could be a lot of people who say that they will support the new set by buying a box of packs, but then when the time comes they don't have $150, and so they drop out. Do you know of a way to prevent that sort of problem?