Need Help! Resin block for milling

I have acquired some samples of 'Sika block' from a friend. He cannot remember where these samples came from. The material feels like plastic, I think it is some kind of resin block and it is designed to be milled.

I have been working on a project where I am regularly prototyping plastic moulds. I have been using Nylon, however this does not machine very nicely. I had a go at machining this 'Sika block' material and it does machines well

Does anyone know of anywhere I can buy some resin block material, something similar to Sika block which is designed for milling?

Thanks
Jack