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.