I get in the same situation all the time. Right now I have a K98 and a Romanian M-44 in parts hiding in various areas of my workshop and garage. I have to work on cleaning them up on the sly. I have a few things going or me though: I have quite a few surplus rifles and they all look pretty much the same, she doesn't have an accurate count of how many rifles I have, if she ever makes a connection that there's an extra rifle in the cabinet or in the workshop, I can say "oh, I had that one for a long time."
Roses and diamonds do help.

Alcohol, Tobacco, and Firearms... who's bringing the chips?