Are there any C8 or C10 lights that are XR-E single mode?
Also, has anyone found any aspheric lenses that are more or less ready to just drop in for this size light (meaning diameter and back focal length appropriate)?
While Iām at it 
are there any C8/C10 lights with smooth rather than crenelated bezels?
I've looked for 1 mode XRE C8 inn the past with no luck.
Now I just swap out the driver with one that is one mode or next best thing. The XREs I mount on the rifles gets 1 mode 1A driver from DX or 2 modes (High & Med) 2.1A V2 driver from kaidomain.
In my small sun c10 i use a direct drive driver with all components removed which in turn gives one mode.
Havent seen many lights at all with single mode driver.
Not sure if this is what you want but the trustfire TE-R2 from Manafont is about $25 and takes a standard P60 pill. The bezel is crenulated, but not aggressive.
I have one, and it seems to be OK for quality with a nice beam. Some have mentioned the plastic retaining ring in the tailcap but it hasn't given me any trouble.
This light comes with a 5 mode XR-E but if you really want a single mode, salvage this pill for another project and fit a custom single-mode from E1320 or others.
Due to the design, the heatsinking seems pretty good. I fitted an Intl-Outdoor XM-L pill in mine (2.5A) and haven't had any heating issues. A hard-driven XR-E or XP-E would work pretty well I'd think.
Don't know about aspherics though.
Food for thought