Hi Brian,
If you have access to a treadmill, you could crank up the incline. Another suggestion is a parking garage. Those ramps are good hills.
With that being said, if you don’t have access to any of these the toughest hill in the NYC marathon is technically mile 1 but you won’t notice it with the excitement. Personally, I find the Queensboro bridge (mile 15) to be the most challenging. No one will judge you if you slow down or even walk up the bridges.
The other elevation challenge is slight (on a normal run I hardly notice I’m going slightly uphill – advantage being a Manhattanite) but noticeable when you are at mile 22-24 right before you enter the Park.
I hope this helps. Also, happy to answer any NYC/race day logistics.
Good luck with the rest of training and see you in the start village on November 5!