Reddit mentions of iExcell 50 Pcs 2"/51mm Steel Alligator Clips Crocodile Clamps,Silver Tone Nickel Plated, Come in a Plastic Case

You can take them apart by just drilling out the rivets, and I just use spray paint for the base color. You can use some kind of paint stripper (can grab some from your local hardware store or walmart, but something like this) to remove the paint that is on there if you want, but it's not completely necessary, just make sure you do light coats of spray paint so it sticks nicely.

For the details I use paint pens but you could probably use any paint with fine paint brushes.

Then i finish with a glossy enamel clear coat spray, and just be careful not to spray it on too thick or it can make the paint run or bubble up a bit.

Aside from just "how to do it" some tips:

• It's easy and even if you just want to paint it a solid color it's totally worth it. I haven't done any hot wheels mods before this and my first couple still turned out great.
  
• You can always strip the paint again and start over if something gets screwy
  
• Wait like a full day between the main painting steps (base coats, wait a day, detail work, wait a day, clear coat) just to make sure it's all good and dry
  
• Use gloves when you are doing the detail painting so that oils from your hands don't mess up the base paint
  
• I use some clips like this to hold them up. What works great is putting one of the posts from the body of the car into the round hole on the clip, and then clipping it onto a toilet paper tube. Works great as a little handle and stand.