So I'm looking into starting a cottage food business and the frosting I use is Italian meringue buttercream, and I spoke with my state's agriculture department, and she said that if I can find a legitimate scientific source that states the frosting can be left or for 2 days then I can use it. I looked at Wilton's Italian meringue recipe and they don't specifically state that it can be left out, so I emailed them and I'm waiting for a response back, but I wanted to ask you guys if you by chance know of a legitimate source that I can reference for a Italian meringue buttercream recipe that states it can be left or for 2 days. She said it can't just be any recipe, that is has to be from a legitimate source. Thanks in advance for any help. 

I am not on Cake Central much anymore, and am just today seeing your post.  I hope you have something resolved with the ag department by now. 

If not, or at least for your edification, I found some food safety information on Italian meringue buttercream on Serious Eats.  The bottom line is that when making Italian meringue buttercream, the egg whites are likely not held to a high enough temperature for long enough to pasteurize them, and there is no way to know.  They explain how Swiss meringue IS brought to temp and time with room to spare, to pasteurize the egg whites.  Perhaps you could switch meringues used if you wish to not have to keep your cakes refrigerated?

Good luck with your home cottage venture!

Link to the article:
https://www.seriouseats.com/italian-meringue-buttercream-frosting

I just had a thought...If you really like using Italian meringue buttercream and don't really want to switch, you could use pasteurized egg whites.  I believe they can be purchased already separated from the yolks and pasteurized, or you could pasteurize them yourself. 

Some information on pasteurizing eggs yourself is toward the end of this article:
https://www.melindalee.com/resources/reference-center/about-eggs/

You may need more sources to back up your pasteurizing of eggs at home for the ag dept, I don't know.  But that will be definitely easier to find than food safety regarding Italian meringue was!