Optiscplanet sells a lot of spotting scopes as does B&H.
A four inch objective lens is a bit hard to mount to a rifle and would make the rifle seriously top-heavy. Spotting scopes can be had half that size (1/4 the lens area), but the bigger ones are a lot brighter at the beginning and end of day. But the big ones get way too heavy for packing and day hikes. Here's a 95 mm Swarovski. You can get a fairly decent used car with high miles for the price of this scope!
