There are very few good sources to find specific groups of sites that accept guest blogs. My advice is to find blogs you like and respect and email them to see if they accept guest blogs. For example, my site at Magolnick.com sees a few thousand visitors per day and I'm always looking for good marketing content.
I think you should be asking a different question.
Why would a popular marketing blog want you to do a guest blog for them?
(To clarify, I'm assuming you're not a popular marketing/business/tech guest blogger, otherwise you wouldn't be asking this, because the other top bloggers would know who you are and a simple email or call would be all it takes to initial a guest authorship opportunity.)
Guest blogging is about networking.
1. First, do your homework to discover which blogs have more traffic and active readers than you do. Google will give you blogs to start researching, then you can look at their Alexa traffic rank, how many social shares they get and how many comments they get, among other things, to determine how popular your blog is.
Focus on blogs that have higher engagement and traffic than yours.
Keep in mind that you're actually looking for readers (who I imagine you'll nurture to become customers or use to negotiate ad rates), so don't focus on just tech blogs.
Also, be willing to expand your topic - the goal is to get readers, not share your opinion on app marketing tips.
2. Connect these influencers using the social web. An easy way to start is to pick 10 blogs that you want to write for, and focus on getting on their radar. Respond to their tweets. Share their posts. Comment on their blog. And if possible, purposely bump into them at networking events (you can tell which ones they'll be at from their social profiles).
3. Eventually you'll get to a point when they'll notice you. And you can strike up a conversation.
The most important thing is to give before you ask. Otherwise you'll get nothing.
(Examples of giving: Share their post. Highlight a post of theirs in your blog post and send them an email thanking them for writing the article, without sending them the link and asking for a share. Mention them on Twitter. Etc...)
Relationships take time to build, and they're worth it. I would focus on building a network with other bloggers, the guest blogging will come naturally.
Best of luck.