Unfortunately, you are having trouble finding this device color because it was not produced by Apple. The Mini 4 was released in Space Gray, Silver, & Gold (please see source below- and yes i'm calling wikipedia a source :rotfl
There are custom sites that would be able to get close to that color, but you will pay a premium to do a custom order. Colorware is really the gold standard for these types of custom projects. I'm not sure what the pricing would look like as you would need to get a quote through them.
I'm sure the size of the mini is very inciting. But, if you consider doing a custom project your budget will most likely jump into that iPad Pro range. The 9.7" iPad pro is available in Rose Gold as a stock color option.
Last thing to consider would be case or skin options to try and capture that particular color type. This would be the most cost effective option. Let us know if you'd like recommendations on this. I'm sure the team would love to chime in!