I plan to be doing more sparring outdoors come March & onward, and I've occasionally seen clips on YouTube of people wearing shin/insteps that fit over their shoes. So...like...where do they get those?

After much Googling, all I've found are these: http://karateinsider.com/grappling_sd_shin_guard_shoe.htm

Has anyone actually used these and can tell me how thick/shock absorbent they are? The fact they're 1-size only kind-of turns me off. I won't just be buying for myself and I don't see me (let alone people bigger than me) and people who have significantly shorter/thinner legs fitting into the same size shin guards.

Anyone have any leads? Even if they're not specifically intended for shoe-use, whatever works for that purpose will work.

Have you considered just using a pair of straight-up shinguards, without the instep protection? They'll be a lot cheaper.
The top of your shoe should be enough to protect your foot, and well... instep kicks tend not to the be the damaging ones.
Also, sparring with shoes on is AWESOME. The extra protection of the foot allows you to kick a lot less conservatively than you would barefoot - or even with instep guards. You can kick with a lot more parts of your foot, as well, as strikes with the toe of the shoe now become a viable option rather than a recipe for broken toes.
I miss sparring with shoes on. :{

I have considered it. Ringside has a $23 shin-only pad that looks at least fairly thick (I really would like something thicker than $10 cloth ones to protect people's ribs from my shin), which is my backup to try if I can't find something I like with an instep that works with shoes.

Also, yes, with my running sneakers on I can totally open up a can of Savate (the toes are perfect for it actually), but I'm on the fence in regards to encouraging people to do it since the the headgear we're going to use (which is a must for other reasons) has almost no padding on the sides.

Savate, anyone?

Those are designed by Revgear. One of their very first products.

www.revgear.com

Those things can take some serious impact. You have to mold them first (like a baseball glove) but they fit fine afterwards.

Thanks, that's encouraging to hear. I'm going going to at least buy a pair for myself next paycheck and give them a test-run.