@ngtechzone I would recommend start by adding an Advertisement page on your blog. I have not seen a good alternative to BuySellAds so far. Though it's a good idea to list your blog on those alternative marketplace as suggested by @mybloggertricks
But you should do following to get direct advertisement
1) Add an advertise page on your blog. This is also known as Media-kit. Read about how to write a good media kit on your blog.
2) Check out other blog in the same niche as yours. If you see direct advertisers there, click on the advertisement & go to advertiser website. Use contact form and tell them about your blog/website & open slot for advertisement. This is hit & trial but at the end it will work.