I've never encountered one. Pretty much all the AM3+ motherboards were designed back around 2012 when that wasn't a thing. Even the number of AM3+ motherboard that had RGB lighting at all is relatively light; it was few enough that boards like the ASUS 970 Pro Gaming Aura put it in the name.
Honestly, even if such a thing does exist, it would be quite obscure and difficult to find in the secondary markets at this point. Not to mention the wisdom of dropping $150+ on an antiquated 2012 platform just to get addressable RGB headers.