I've done over 400 free speaking engagements for corporations, in exchange for the opportunity to promote my services (personal training). Now, I'd like to start doing paid speaking gigs. I've done 4 paid speaking engagements in the past, but they kind of just fell into my lap. I'd like to be more deliberate about it.
I'd create a website about yourself. List the previous free speaking engagements you have done, maybe in a portfolio style.
Create a blog and begin content marketing. Answer questions companies are researching on Google about hiring a speaker. Rank for those keywords and the organic traffic will come in and people will find out about you on autopilot. That is the beauty of proper SEO done right.
You could also have each previous speaking engagement be its own blog post and rank for the topics you were speaking about. That is the strategy I would go with.
Have calls to action on your website to get them to schedule a consultation over the phone with you for a paid speaking gig.
If you do this right you will have an automatic system in place that pulls prospects in and closes them as they read your blog posts and see that you know what you are talking about.