Guest Blogging Problem?

This link was offered by someone in your original post. It's still a very good starting place:
» 500+ Places to Syndicate Your Content

Have you tried some of the search strings suggested there? They suggest 52 different search strings that are likely to bring up thousands of sites and blogs that will accept guest blogging or article syndication. Surely you haven't exhausted every one of these!

If you want to find sites targeted to your niche, try searching in Google with something like this:
“Guest Bloggers Wanted” + "your keyword for your niche"

Do that with all the search strings. Try four or five different but relevant keywords. That will give you several hundred different search strings, which will surely yield a multitude of possibilities for you.

One other thing you should have in place is this: only offer high quality articles written for people - not mercilessly written for search engines - and write long articles of at least 1,000 words. This will help to guarantee acceptance. Mention this in your initial query.

If you are offering a guest post of 400 words long that has a main keyword inserted to a 5% density, or whatever, don't be surprised if no one wants to publish it. Write for people and ignore keyword densities, or any other SEO considerations, and write lengthy pieces that are engaging and entertaining. If you can't do that, find someone who can write them for you. There's always a way to get over every hurdle.

The trick with this, and so many other things in life, is to never give up. Persevere and you will get there!

John.