I just spoke at length with the Sprint international department, provided SKUs and so on and got a smattering of misinformation. The first guy I spoke to said the computer wouldn't let him ship the SIM card so I talked to his supervisor. His supervisor insisted that the Nexus 5 I ordered through Google is GSM and since Sprint is CDMA it won't work. He advised me to order the "Sprint version" through Sprint directly. Then when I pointed out that's wrong he said that Google is including everything you need to activate, and that they only use SIM cards for international travel. So I said I need it for international use (my account would show that I've used my phone recently in Canada and Japan). He tried to process it but said it wouldn't go through so I need to go to a Sprint store for a SIM card because International Services doesn't ship SIM cards, only activates them.
Then the icing on the cake: he told me that he had ordered his Nexus 5 from Google yesterday.
So hopefully the situation will be sorted by the time my N5 shows up and I can either waltz in to a Sprint store and procure a SIM card or Google is indeed including all the necessities for activation in the box.