I didn't mean in regards to the Challenge System - that was his D&D simplification attempt back in the 80s that I wish I had a copy of. (Honestly I wish both that and his Lords of Creation were available for sale as PDFs both for historical relevance and to actually have a wider audience for - the fact that he was kind of OSRing D&D before it was even in it's 2nd edition is an interesting case study I think - but that's another story).I don't think it was actually was originally online. I think it was just something he developed (in 1986, so really unlikely to been online) that has been passed around online. I'm not finding where or how it might have been published, only that it supposedly was (a zine maybe? It's too long for most magazine articles, too short for a book).
I meant some kind of sarcastic response to D&D 3e - I'm wondering if the OP might be thinking of someone else associated with early D&D rather than Moldvay penning a sarcastic response to D&D 3e. There are a few people I can think of who would have been online during the 3e rollout/heyday and also would have had the personality to pen a sarcastic response to it, but Moldvay isn't one of them.