Hello nana, I really hope someone can help you better than me, but this is a difficult one. Ise jingu is one of the few places that make the omamori in-house as far as I know.
But most omamori sacks and the paper inside it (ofuda), which you should not open and read, has been assigned by the jinja to the local business, and it has been like this for centures.
From the way you wrote it, I believe you know that already. So I believe it is difficult to find special cases like the Ise Grand Shrine.
The way I like to see it, is that all omamori are authentic and sacred, as long as they are blessed by the temple before it is sold.
Sorry for not being more of a help I hope someone else knows more!
Hi, I have read that most omamori are mass produced by factories then blessed by shrines and temples, is there anywhere in Kansai apart from Ise Grand Shrine where I can find omamori which is handmade by the shrine itself? Thank you!