Nope - they won''t send them. We are in Canada, and I drove over to get US stamps for the US rsvps. The guests from Europe had to put their own postage on.
They will not mail it for you. I sent my invites overseas without return postage and put a handwritten note for my guest to email me instead so they would not have to incur a cost.
I just looked into this because I have guests overseas. You have to go to the post office and buy a coupon (I forget what they''re called). They cost $2.10 right now, and you would send it to your guests who would then take it to their post office to exchange it for a stamp. I think that sounds like more of a pain than just asking my overseas guests to put on their own stamp...