Do you mean a threaded funnel, one to screw on instead of the cap?
Yes, but threaded to fit a standard water bottle, if those threads are standard. Or a 2-liter bottle. I thought that I had found such a thing and ordered some, but it turned out the threads didn't match a water bottle, but were intended to thread onto a 16 ounce generic spray bottle one might use for a cleaning product.
I'd be willing to offer half a bitcoin for one, shipped to zip code 40214
The idea is to be able to refill common water bottles with something other than water, such as milk.