Have a look on eBay - I've had a dug around and there are plenty of currency bundles from Germany, Zimbabwe, and Venezuela.
Ironically though, given that everyone is trying to collect this stuff now, the prices of high notes can get quite absurd. E.g. I've seen $100 trillion notes being listed at more than $300 USD apiece and that seems to be the going market rate.
Definitely not a great buy imo. Just accept a slightly lower denomination (still in the billions/millions) and move on.
Just checked eBay, yeah the prices seem to be quite large haha. I also checked local cash currency exchanges here in NZ, and none that I could find could swap to any of those currencies

I'm talking to stackitup though, hopefully I can get some off him
