Oh man, that stinks. As a Vita owner, I understand the pain of buying memory for that thing. When rumors first surfaced of the Vita store shutting down, I bought a 32 GB card right away and I am glad I did. They really jumped in price when Sony made the news official. I can't quite fit all my stuff on there but it was a good chance to cull the digital collection of some PS+ games I will never actually play.
I hope you find something to replace it with. I'd love to do the jailbreak to use SD cards but I'm too worried about messing up my system. Fingers crossed my 32 GB card keeps working.