Well, a high quality true mixte in a large size may be a challenge but step throughs like the more common hybrid style I ride are more common.

Here's one but probably too small: https://vancouver.craigslist.ca/van/bik/5990679514.html

Here's another: https://vancouver.craigslist.ca/van/bik/6025035969.html

Too bad you could not mash both together. One looks like it has a chromo frame and nice looking rims, the other has drop bars and maybe a bit bigger sizing.

Now, if you have 3K you can take a local bike building course at the UFV Abbotsford Airport campus with Paul Brodie and build your own step through as part of the course. It's what I'd be doing with my holidays if I had a few extra K's kicking around

Bike frame building 101 - University of the Fraser Valley (UFV)