I've found Nightwood to be accommodating with vegan requests. I also once reached out to Big Jones and they said they could accommodate a vegan diner, though that was some years ago.
Here are some other suggestions that I haven't tried personally but may be worth reaching out to:
Boka (I believe they have a vegan entree on the current menu)
Perennial Virant
Cicchetti (they have a daily vegetarian preparation, so could possibly do vegan)
Taxim (they have lots of vegan small plates and I think might be willing to do a vegan entree)
Trenchermen
Embeya
Kinmont (this is a newly opened seafood restaurant, so it may be a longshot. However, I dined there recently and found their vegetarian/vegan side dishes to be outstanding and the management followed up with us after we dined for feedback, so they may be eager to accommodate)
Nellcote
The Bristol
Anteprima
Unite Urban Grill (this place is new and isn't quite as upscale as the other restaurants mentioned, but their menu is already pretty vegetarian-friendly)