I had some minis that I had painstakingly painted and based, only to have the rules change and I needed to change them too bigger bases. 

Rather than destroy all that hard work, I decided to make some adapters, and thought others might find them useful.

Currently made up;

25mm --> 32mm
25mm --> 28.5mm
28mm --> 32mm
32mm --> 40mm

But let me know if you need different sizes and I will happily make up that size for you too. 

Please note: The mini in the second photo is just to show how the adapter works, and is not included in the sale