Some recent non-urban new builds in Utah, which are a mix of Sprint conversions and new site builds:
I'm also hearing of future new site builds in places that currently have weak / no signal on all carriers like Fountain Green, Oak City, Woodland, and along Hwy 191 in the canyon north of Helper by the Power Plant. There are also an unbelievable number of Sprint conversions happening in the urban Wasatch Front corridor as well.
Only time I have gotten a free sim from them is when I "purchased" some "free" phones from T-Mobile, unless I go back to when they were a distant 4th carrier. My four other MVNOs are feast or famine, so I try to keep several hanging around. I have noticed different versions have different capabilities, and newer is not always better. They typically force you to upgrade when you need to activate another discount period.
Hard to imagine they're actually worth much as easy as they are to get free though.....they keep sending them out unsolicited like nuts. We just got like a 3rd packet of them less than a month ago and got another email notifying "SIM card is on the way".
E-bay. The physical sims do have one advantage: they are not tied to your phone, thus you can change phones mostly without your carriers permission (except Sprint billing). Benefits signal hunters, travellers, and thieves.