Show, Dont' Tell.
Write. Start a Blog. I recently hired someone remote and one of the reasons was their blog (among other reasons). I could go through their posts and see how they think, their perspectives on stuff and skills in writing about it. The best way to market yourself is to distinguish yourself from others as much as possible. I am always amazed to find people who are freelancers/consultants but don't have a good online presence. Yes it is hard and yes it takes time. But that is the point.
So don't print business cards. Well ok print them but that should not be your priority. I run a business and I failed to print business cards so far (too lazy). But I still meet plenty of people online and in person. Start writing about whatever you know. It doesn't have to be perfect. It doesn't have to a scientific paper. Just write.
You mentioned sysadmin, cloud stuff, migration etc. Do you know how critical this stuff is for any business ? If you kick ass on this stuff, you already are ahead. But Show, don't tell. And no, there is no easy way. No one cares how good you are because no one knows.
EDIT: I forgot to add that I also recently hired another short term consultant for a gig. This will make them a few thousand bucks and I found them online through their website/blog AND they wrote an e-book on the subject. Easy win for that consultant since I emailed him saying "take my money".