I'm thinking maybe it was offered directly from Craig? Probably not, but I'm thinking now to go look for his website?
I just visited and still found nothing, but on another tack, I found a PRODUCT on the Presonus page which is for a purchase of Anderton's IRs...
https://shop.presonus.com/Craig-Anderton-Surreal-Reverb-Impulse-Responses
So, maybe this is why there's nowhere to find free Anderton IRs?
...and now I found this. The link to download leads to a 401 error message...
https://noelborthwick.com/cakewalk/category/industry-news/