Alert based on number of sales

Hey, 

Long time lurker, first time poster. 

I've done about as much searching and scrolling as I can manage and hoping someone can point me in the right direction as I cant find anything. (If I could code I might make a stab at it.) 

I'm looking for a way to alert me (via email probably) when x number of sales of a certain item have been made. Purpose is to automate reordering parts for items I make and sell. 

For example, once 100 orders of item come in I know I have to reorder 120 items worth of part as I average 20 orders a week and it takes 5 days to arrive. 

This would then need to reset for the next 100 orders once I have the new materials in. 

I'm hoping to not pay for this. Is there an email alert or similar I can set up in Squarespace that I'm completely missing?? 

Andy x

I've not heard of that as a feature, but you can set a low stock alert at user defined threshold:

Stock level alert email

This isn't exactly what you're asking for, but you may be able to utilise it to achieve something similar.