From memory there is a Po-40 aftermarket kit for the 2IS to add auto fold. Maybe it might work or be able to be adapted to suit 3IS?
Or a universal kit like this https://www.ebay.com.au/itm/Universa...-/111016438613

 

for those that have the retracting mirror button, what year and model IS do you have? was it included in the luxury package? it looks like only the overseas models had the auto retract available. any help would be appreciated...I'd even take the part number if you had it handy. thanks in advance!