True primer will work better because the particles of pigment are usually smaller than in regular paint. They won't fill in the smaller detail as much. If you can't get primer, then use what you can get. I know that some people use automotive primers or Krylon laquer.
I wouldn't recommend priming with acrylic though, use enamel or laquer. One of the main reasons for priming is to give the final coats of paint something to adhere to and enamel or laquer will adhere to the plastic much stronger than acrylic would.