I've actually been looking for the same sort of thing, but haven't bought any of them yet, since I haven't started on the actual dress portion of the costume.
In my search, I've found some options for white eyelashes, and white mascara.
Eyelashes I've found that most of them are ridiculously costume looking, or over the top feathers and glitter.
are on the simpler end, and could work nicely if trimmed back a bit.
are a bit warmer, since they're an ivory white instead of snow white. Not what I'm looking for, but they might suit your look.
As far as the mascara goes, I've found that a lot of the lash primers seem to come up a lot, but I haven't played around with them yet, so I don't know if they're actually white.
is the one really stark white marscara I've seen online in my searches. Not a brand I'm familiar with, and doesn't look like there's many reviews.
I'm considering this
one for my uses, since it'll give that frosted eyelash look, instead of feathers or just white.
Most of the stuff I've browsed is from Amazon, but I have checked out some stuff online from Sephora and places like that... which could be another option, instead of shopping online, check out the brick and mortar storefront - they may be able to help you out and let you see how things look.
I wish I could say I've tried some of it, but I'm just in the research stage, too. Hope some of the links I've collected are helpful enough to point you in the right direction (I'll be watching to see if the experts on the board have some better suggestions, too).