Is it based on the tech on their website, or is it private tech? I have experience identifying IBM ODM users, which is not public, and identifying sites.

IF IT'S A WEBSITE:
What technologies specifically indicate a good fit company? Azure? .NET? etc. Let me know in a private message. Once I know that there are a variety of avenues we could use to uncover the companies which are relevant.

IF IT'S AN INTERNAL COMPANY TECH
Here we base the identification heavily on partnerships. Naturally, your dream partner here would be Microsoft sending you leads. There are ways to work up the chain there, but it's an all-or-nothing outcome - either they work with you or they don't. Putting all the eggs in that basket is risky. The next type are complimentary companies who could provide referrals from their existing client and prospect base to you for a commission on any new business you close. The development of referral partners is complex but powerful.

If you need help developing a specific strategy just suggest a few times to talk.

One of the easiest way is to reach out to MVP's and get connections from them on who use Microsoft Stack.

http://mvp.microsoft.com/en-US/default.aspx

You can use an online service called http://builtwith.com/. This can analyze the technology stack of any company and can also provide you with meaningful reports. It has a free and a paid version - you can also search by technology and find e.g. companies in US that are using Azure.
Let me know if I can be of more help -

Building list of specific technology users can be hard, so you need a software that enriches the lead base with technology usage signals. I describe one of such examples here: https://youtu.be/2ZvVc_rCNXk