Here are a few options:
1. Use motion effects in Avid Xpress. You can’t keyframe these to change speed over time but you can cut from one speed to another, or dissolve from one to another. Not recommended.
2. If you have a decent budget for this upgrade to Media Composer Software. It will allow you to keyframe your timewarp effects and do exactly what you’re wanting, plus you get a lot of other stuff. This will set you back a few grand though for the upgrade ($3,000 maybe?). https://www.avid.com/promos/xproMoveUp/
3. Boris offers some timewarp effects via RED for sure. Possibly some of their other packages offer time remapping as well? http://www.borisfx.com
4. 3Prong’s SpeedRamp. I haven’t used this exact plugin, but i have their ColorFix effect and it’s really nice. You can download a demo to try out. Very reasonably priced too. http://www.3prong.com
5. After Effects. Export your clips as a Qtime or Qtime reference file (if you AE is on the same machine), then do your motion effects there. http://www.adobe.com
These are off the top of my head. There may be other plugins that offer time remapping too, but at least this list will get you started on your search. Good luck!
Michael.