You can get them through purchasing them from player shops and from voting - you'll get one every 20 days. Sometimes they're prizes at events, though that's rare.
You can always visit the Wiki to find out more about these kinds of items Link here: http://empireminecraft.com/wiki/vault-voucher/ Also, please try not to double post, forum specific rules says that double posting (two posts within short time frame of each other) are considered spam. As for where to buy them, though, there's a few places I can think of off the top of my head: My Museum at 18200 on SMP9 AlexChance's Shop at 4005 on SMP2 iGTR's Shop at 123 on SMP1 I am very sure that there are many other places and they come up on community auctions all the time so you won't have any trouble finding a voucher if you want one - though you can alternatively use the /vault expand command as previously mentioned
Also: mini bosses. If you fight Momentus on diff. 7 and up then there's a good chance it'll drop these. Hmm, this gives me an interesting idea for the wiki, will have to check up on that.
10k-15k depending on server and demand at the moment i sell mine expensive on 12249 (smp6) but i have about 2 stacks cause i buy them for 11k
But we're talking about Vault Vouchers, that's what this thread is about. The Vouchers cost a bit more because they can be collectible.
You can expand your vault an infinite amount of times. Since you're a diamond supporter, you can do /vault expand until you get 50 vault pages. Then you can use vault vouchers to continue expanding.
I wasnt asking me was I? I was asking a regular member. Who would do it 5 times then hit their limit thus needing vouchers. Hence explaining why they go for more then 10k
