How do I validate an idea when my target market (big companies) are unavailable to talk to me?

First, perhaps you're overreaching. Do you have proof of concept or not? If you don't then you need to work your way up the ladder. Try dropping your target 2 levels down at first, and as you build up a roster of "wins" start to set your sights on higher and higher levels of business. If 2 levels down is still impossible to reach, then you may need to go even lower down.

And at least some of the issue is that you haven't gotten creative enough with how you're looking. You're saying you can't even find a name in the organization? You need to know which department you need to get in front of. Then you have to do some Sherlock Holmes tricks to find names within the organization. Now, you need to figure out how to get an introduction to the people behind those names.

Negativity will get you nowhere. This is an exciting adventure. If it's so easy to get an interview with the Queen — if that's where your social circles go — then I bet that she could make some introductions for you. If not, you have to look from where you are now to a path to where you want to go, and stop trying to skip ahead. Find the person who knows/likes/trusts you with the highest ranking business in your circle of influence, and get into THEIR company to prove what you do. Then ask them to recommend 3 of their suppliers, collaborators or allies in the business world to recommend you to. Climb the ladder.

I help people with business brainstorming sessions — strategy and creativity. I may not be the right fit for you if you want to come up with ideas and strategies, but hopefully these ideas are helpful to get you moving. Oh, and having said that — get moving and keep moving. No more negativity because that shuts down your creativity and makes you feel helpless. You're not helpless. Start from where you are, the reach you already have, then STRETCH that reach. Stop trying to teleport to somewhere where you have no influence.

This is your validation. It is telling you that, for now, big companies are not your target market.

Your initial target market should be people that you can reach. For example, if you can get small businesses to talk to you, then make them your target market, and validate ideas to serve them.

If you really want to work with big companies, then still follow this advice and find another target market (such as small businesses). Once you have success with SOME target market, you can use your existing customers (who know and trust you) to refer you to buyers in your preferred market (big companies). Also, remember that people change jobs. A customer who works at a small company can go to work for a large company.