I don't think Glock makes anything single stack...
Ever heard of a Glock 36?
... I have now!
I'm pretty sure Glock isn't worried about competition at the moment, nor the cost to redesign. Glock designers would have the new pistol designed in less then a week and could probably be in production within the month if they really wanted to
Google: G30S (gen4)
Should be a pretty good seller