Yes, he plain wire ones would be easy to make but the proper ones are 3mm steel which has been tempered a bit like spring steel to resist bending when hit. - try straightening out a factory made one and you will see what I mean. This is also why the coil on the top retains its strength as a springy clip.
Someone must have bought these recently, there are thousands out there.
Anyone help? Just to recap, trials marker pin, approx 450-500 mm long, 3mm steel wire with a 50mm loop on top to clip a card in. Need around 200. Where did you get yours from, and a supplier contact number or email address would be great. Cheers guys.