Logic Express (made by apple) is a good bet, and cheap at $150 otherwise there’s Ableton Live, which is a bit more expensive but gets my recommendation. Note that these are full featured programs, though, with more than just sequencing built in. If you’re just looking for something for free, I’d look into downloading hydrogen and a few sample packs.

There isn’t really a specific sequencer that makes 60’s pop rock and only 60’s pop rock, most are going to be like Logic or Ableton and be versatile as long as you have the right samples.