Thanks everyone!
It sounds like the general consensus is factory Ruger 10-22 magazines are the most reliable, and I know of a gun store in town that sells them in 3 magazine blister packs. So, the next time we get to town, I'll buy a pack of them.
I wasn't going to buy 3 more Ruger 10-22, 10-round magazines, but now that I've thought about it, my wife's Ruger "American Rimfire" uses the same magazines, so I might as
well buy 3 of them. We've been out shooting ground squirrels over on our friend's ranch again this spring, and while the extended magazines for our rifles come in handy when there's ground squirrels popping up all over the place, they often get in the way when we're trying to rest our rifles on top of fence posts.
Fence posts are the "norm" when it comes to rifle rests where we're exterminating ground squirrels again this spring. Last spring was dryer and we could sit or kneel down to shoot, but there's still a lot of snow and mud out there this spring, so we do most of our shooting standing up. We both have monopods, but fence posts are better.