Are there any secrets to cold "calling" possible advertisers?

Here's the situation, I am organizing a small indie science magazine and to subsidize the cost to print and deliver the magazine and compensate writers, I need to sell advertising. So far what I have been doing is making a list of companies I think have a product that my target audience would be interested. Then going to their website and emailing them using the most relevant address I can find on their site. I am really new to this and not entirely comfortable asking for money, does anyone have some advice on how to make cold calling less painful and/or more efficient?

Also here's one of the emails I sent. It was to a popular electronic kit company. They replied with "not right now, keep us updated".
Quote:
Hello [redacted],
My name is Jacob Shiach and I recently started a magazine called The Citizen Science Quarterly.
With the goal of featuring citizen scientists doing amazing things in their home "labs" (aka garages,closets). As
well as educating people as to how they can get started doing real science.

Other than being really excited about the magazine and telling everyone about it.
The reason I am contacting ya'll is to see if you would be interested in sponsoring the magazine in some way.




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