For example, something along the lines of the professionalism of:
Stackoverflow has a jobs page. This link is to a search with keyword
freelandr offers you to `Land your next Freelance Job'.
Here are two specialised job agencies, although I don't know if they relay freelance opportunities.
We are well aware of the data scientist being the sexiest job of the 21st century. JamieAi harnessing this fact connects technical talent with data-oriented jobs organizations of all types and sizes. The start-up firm has combined AI insights and human oversight to reduce hiring costs and eliminate bias. Also, third party recruitment agencies are removed from the process to boost transparency and efficiency in the path to employment. Another example is Woo.io, a marketplace for matching tech professionals and companies. https://hub.packtpub.com/25-startups-machine-learning-differently-2018/
R-users specialises in the language R.
Kaggle is more contest platform with a jobs board more than a freelance platform. Try upwork and freelancer.com. They are the ebay of freelancing and they support a wide range of payments although some of their fees have been going up for a while and search is favoring fees over matching to best results. Still you will be able to sort by skills like visualization, machine learning, data cleaning. It will depend on what skills you have to offer. I'm sure there are others better out there and probably others without too much traction. AngelList also offer contracts for data scientists if you're looking for something more structured.