Almost all high security manufacturers have patents that protect their keyblanks from aftermarket reproduction. That means you can only get the blanks from the manufacturer. This also means that it’s in the best interests of the manufacturer to only deal with reputable shops that will protect the integrity of the high security system (under penalties that range from legal action to at very least, they are not longer allowed to sell/service the product.)
The shops are often also only dealing with one or two “keyways” from particular manufacturers that are geographically distant from other shops that might deal in the keyshape. This makes it highly unlikely that a shop COULD cut a high security key, even if they wanted to break the manufacturers agreement, because the only keyshapes in the area are likely controlled by only one reputable shop.
And under no circumstance would a manufacturer let their keyblanks be compromised in a situation that allows the general public access to them uncut (as a self service would have) because it would make hand filing or machine cutting surreptitiously way too easy to do. That compromises the integrity of the manufacturers product as a whole.