Anyone know where I can buy those metal clips that the 10mm screw goes into, to hold the splash guard in place under the engine?

I've seen kits and the like on Amazon, but unsure of the correct sizing needed?

One of the common names for these clips - Spire nuts - a general search for 10 mm spire nuts should result in finding numerous suppliers, hope this helps, they are quite cheap when you buy a pack.

I replaced mine with stainless clips, there are different sized clips on the under radiator shield, so I bought a pack of mixed size clips. The ones I purchased are spire clips which require a conventional screw (or bolt as some call them) so get a pack of those as well.
I'm not sure what the clips that take a self tapping style screw are called. but the screws are not so easy to find in stainless.
I would also recommend using a touch of thread lock as they do not lock like the self tapping screws.

David Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

Previous Cars of note
Land Rover Discovery 2
Jaguar Mk2 3.8 - Company car
MG Midget 1974 - Concours

Thank you gents.

I found a part # SYH500040 for the clips.

I bought 3 of them at my local dealer for........$10 CDN!!!

It is what it is, I like my vehicles to be perfect!