Based on past years, they are not consistent with when the Dessert Party dates come out. Possibly as a result of MNSSHP, but it can't hurt to call to see if a CM has more information than the website. And - I'm not sure - but dates might come out at the 60-day mark instead of 180.
It's available up until Sept 28, so it's not the 60 day thing. I guess they are just being slow to load it? That's frustrating, because it means I have to keep checking!
It is weird that the wishes dessert parties are not available for October yet. I would think it would be soon. The Hallowishes dessert parties have been released, so you can book for party nights if that is what you were planning.