You can buy them on Amazon and get two-day delivery. These are what I use. They aren't genuine, but they work for my projects.
Sounds like - if you believe Andreas, a decent 1 mF aluminium electrolytic across the 3.3 V terminal and ground would make the choice of regulator moot and any one as good as any other.
If I have to order a capacitor, I assume a 6.3V rating would be better than something higher - less resistance, more responsive, and of course smaller.