I've love advice on both fronts! We do know someone whose dogs will play fetch, but our schedules don't click enough and we see them maybe once every few months. I would love to hear about what I can do with Pebbles when her "fetching" friends are busy
Shelties are just too smart.

I'll tell you what we did with Koji (the younger of the two), in case you see your fetching friends soon. You got a lot of other great advice for when you dont' see them.
Hopefully her friends aren't huge dogs.
I held Koji with one arm, while throwing a ball to Miko. I'd give Koji the ball, tug on it, pull it away from him, show Miko, get him to tug a bit, then throw it. I was trying to build some drive with Koji, and he wanted to run after it badly, but I held onto him so he could "observe". Miko would bring it back, I'd tug, praise, and throw it again. After doing this about 6 times, Koji was going crazy so I finally held onto Miko and let Koji go run after the ball. He brought it straight back to me, where I immediately tugged on it with him and praised him. Then held him and threw it for Miko again.
I repeated this about 3 times before I just let Koji go fetch the ball and he's never NOT brought it back since.
I've taught other Shelties this too, by restraining the dog learning, but building drive by playing with it too. I dunno. They seem to get it faster that way IMHO.
(even my breeder wondered how I got them to fetch. But since XH taught Miko and I didn't watch, I have no idea how to start a complete newbie. I only know how to teach by watching)
Oh yeah, I think Koji was only 8 weeks when we started teaching him...he also learned to go on the grass and walk on a leash by watching Miko. So, I'm a firm believer in Monkey See, Monkey Do.
Good luck.