Reddit mentions of Tagua BH1-467 Thumb Break Belt Holster, Sig P-938, Brown, Right Hand

If you are feeling like you have to start carrying your defensive weapon sooner than later you should know why a "pocket sized" firearm is going to have next to no open carry options. It's because manufactures make stuff for guns that will sell and people don't tend to open carry small guns. You will find that the open carry holster options easily available will expand with the full and midd sized firearms and logically the larger the gun the smaller the concealed carry holster selection shrinks. It's unfortunately just supply and demand. Your best bet is to either buy a second firearm that has a ton of open carry options but also concealable options as well. Mid sized firearms tend to have a good balance between open carry and concealed carry options. You can also custom order something and wait a month or so for a holster company to manufacture something for you which would ideally be "exactly what you had in mind". Or go with one of the few options that sort of matches what you had in mind; I found you something like this:
Tagua BH1-467 Thumb Break Belt Holster, Sig P-938, Brown, Right Hand https://www.amazon.com/dp/B00KDQZZIS/ref=cm_sw_r_cp_api_1midzbQ0XWFVB