I would suspect the reason you don't see a complete model of an airsoft gun is multi-faceted.  Probably the biggest issue is most places that host 3d print models do not allow functional firearms of any kind for 3d printing, even airsoft guns.  The legality of 3d printing a functional gun varies from country to country because the parts can not be detected by metal detectors.  Also, the type of polymers involved in most 3d printed items may not hold up to the forces required under the pressures of a firearm in some cases, so liability also becomes an issue.  If you offer a complete 3d printable airsoft gun, in its entirety, then it malfunctions and injures someone, you could be held liable.  So I just think the legalities involved in those kinds of models might be why it's difficult to find in its entirety.

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