The Optics Warehouse big Nikko one fits the Sightron (tight fit), thats what I use on mine.
No where as good quality as the Butler Creek but it does the job.
I might even have a spare kicking about, I will have a look.
Daystate Mk4 iS ST (Huggett shroud & Mod .20) Lightstream 4.5-14x44 FFP
Daystate Grand Panther (Grand Prix stock, .177) Nikko Stirling Diamond 10-50x60
Daystate Panther (Gary Cane custom stock, .177) Sightron SIII 10-50x60