Maybe I'm looking at things a bit different.
I agree that everyone should carry their own condoms and know what size works for them...to me that's just common courtesy. Especially when you know there's going to be play.
However, when we invite someone to play with us and if it's our rule that condoms are required then, I make sure I have plenty on hand. In fact, I keep them on hand at all times in a range of sizes (flavors and colors

). If we've invited someone to play I don't want a little thing like them not having condoms on hand to spoil my fun. It's no skin off my nose to reach over, grab a handful and tell them to take their pick. Now, if they refuse to wear one, then play time would come to a halt.
So, to answer the question...Would we share our condoms? You bet.
Teresa