A little late here, but I'll add my 2 cents.
I used to ski 120+ days every year in Colorado, thanks to summer skiing. There is plenty of great stuff there.
The best summer skiing can be found at the mountain passes. Park at the top, hike out on one of the ridges, jump the cornice, and drop in. At the bottom, hike out to the road, hitch-hike back to the top, and repeat.
Pikes Peak offers great summer skiing down a variety of steep and not-so-steep chutes. Again this involves hitch hiking. Sometimes you can tag along with groups who are running pick-up truck shuttles, where they take turns driving the bus.
Of course, A-Basin (THE LEGEND) sometimes has skiing well into July or even August in heavy snow years.
There is a guide to summer skiing in Colorado, and a guide right here on Summitpost:
https://www.summitpost.org/north-side-couloirs/189243