I've sent some messages and stuff to see if I can still get it but I think it's too late unfortunately.
The participation medal will be added in the next TF2 update, most likely Halloween. The staff have NO CONTROL over this, so they'll be distributed no sooner than when Valve do the update. Just wait patiently, the medal is coming!
Hey! I have yet to be blessed with the possession of the donation medal. I have a ton of patience but i've seen people already walking around with the medal so i got kind of worried if something went wrong. I donated through scrap.tf.