Are you talking about the plastic push pins or the screws?

For the push pins, I looked around and found that I could buy a bag of a very similar pin (10mm hole) for $8
https://www.amazon.com/gp/product/B00CW9JKU8/

Every time I replace the splash guard I just toss the old push pins. There's absolutely no reason to keep the old ones when they are so cheap.

For the screws, I replace them when I think the old one looks a bit worn of if a shop used a questionable screw. These are also super cheap, but not quite as cheap as the push pins. I don't remember where I found it, but I think they only need like 1 or 2 ft-lb of torque to tighten. If you go overboard it's super easy to strip the plastic. That's probably why people lose them. The following worked perfectly for me.

https://www.amazon.com/gp/product/B0040D0OLS/

I haven't found a replacement for the metal tabs though. You could probably bend some sheet metal but it's not a really elegant solution. If you find replacements, PLEASE let me know.