Side Release Buckle design guide/material?

Stratasys has materials like “digital ABS” and “digital polypro”, which are not the real things but suitable facsimiles that have many of the properties of the real molded material.

The family/trade name for these parts are “fastex buckles”…look up ITW Fastex or ITW Nexus buckles. You might have some luck trying to contact an engineer here. Some of these things are pretty trick.

http://na.itwnexus.com/content/gt-cobra™-loop-body