Great question. The answer is twofold.
First, you need to have a sales rep that knows you, knows you spend a lot of money on gear, and knows what you're into. In other words, a rep that will make you a priority.
Second, that you need to contact that sales rep literally the second you hear even the slightest whisper of a new product that you want. Your rep will probably tell you that they know nothing, but this is either a lie (because they're under NDA) or they haven't spoken to the gear company's rep recently. Usually my rep will say something like, "You know more than me right now but I'll look into it." Then he'll come back a week or so later with a small amount of info, and typically take a preorder.
One trick for you: ask them if they have a SKU. Even if they're under NDA, if they have a SKU, they'll usually take the preorder because you ordered without him breaking the NDA -- you brought up the item and the SKU, not him.
So for this Bogner Snorkler Deluxe here's what I did. There was talk on some FB groups and some gear text threads I'm on where people were saying a 100w Snorkler was coming. Obviously I was intrigued but it wasn't enough for me to do anything at that point. Several months later, a video leaked on Instagram from a Japanese guitar shop showing a Snorkler Deluxe. It was hard to make out the exact features but you could tell it was a bit different looking from the stock Snorkler 50 and clearly some kind of new take on it. BINGO! Called my rep immediately, told him about what I had seen, he said he knew nothing but would look into it. Three or four days later he calls me back, says he talked to Bogner, and it's confirmed; but, they didn't have a SKU yet so he made one, right there on the spot, and took my preorder. He told me I was the very first person in the queue.
That's how you get things like this in advance. I made a video where I talk about about this in the first section @ 0:25 - 6:55:
