I have to admit that I wasn't familiar with poster toss! You can try our Yellow Pages and the vendors were have under the "games'' category. www.ptotoday.com/yellowpages/category/games/
I also did a google search and a few vendor websites popped up, like this one: bestcarnivalgames.com/id63.html, but that isn't a recommendation, as I haven't contacted them directly.
Hopefully this give you something to at least start with, though.
As far as unique ideas the only one I can come up with is having a "book booth" at your carnival. Either have a trade in or collect books before the carnival and "sell" them for a ticket or two. Or have them be a prize for one of the games. Ok, this isn't a unique idea, but I am fresh out! However, you will find lots of great ideas here and on the websites mentioned in this topic.
For a silent auction I'd look for a range of values from high to low to have something for everyone. Try for tickets to sports games local and in state, some local attractions, maybe a "Family Fun Night" package with passes for 4 to the movies, dinner, putt-putt, bowling, etc., "Stay At Home Fun Night" package with movie rental passes with a package of popcorn, cokes, movie candy, and so on, a "spa" package is something I'd bid on, some Christmas items like dishes, and how about if u have a company that decorates trees give u a free decorated tree rental? That's all that spring to mind from past silent auctions I have participated in. Good luck on your's!
