The purple 5K was my white whale for about 4 years until I finally found one on eBay.
The 25Ks are out there in some quantity and you should be able to get one for the right price. The purple 5K and red 10k are extremely rare for some reason but at least you have one of them already. For the most part the people that have those chips in their possession don't want to sell them.
Good luck but also have some patience on finding what you need.