Try to appeal to his philanthropic side. Tell him you are not getting her because you want another, but are trying to save her from a life of the puppymill (which is true).

Explain how she is too small to breed and that it might kill her to give birth. If you already have 5 furbabies, your husband ovbiously has a soft spot in his heart. You just have to know how to stroke that soft spot. I hope he gives in and lets you rehome poor Dee Dee. Keep me posted! Good luck!