If you can form effective local partnerships these can prove invaluable. Local groups or services that work with people of the same mind as Racketball players, those looking for health benefits, community and fun.
U3a - university of the third age
The University of the Third Age cropped up again and again while interviewing leading Racketball club coaches. This project has grown amazingly over the past few years with successful groups now in existence right across the country. With Racketball's target demographic fitting this group perfectly have a look in your local area to see if any groups exist and if they would be interested in adding Racketball to there existing list of activities. https://www.u3a.org.uk/
local physio clinics
I coach out of Nottingham Squash Club and have a great link with a local physio who runs a practice, Mobalise. He know that I will always recommend him to any of my players https://www.moballise.com/ this is easily done as he was my physio throughout my playing career and I think that he is fantastic. I know that he in tern will recommend my Racketball sessions to any of his clients who he thinks might benefit from the added exercise and social side. Any players that he recommends can access a taster session completely free.
The health benefits of Racketball are amazing. Follow this link to see articles from The Guardian, NHS and Forbes magazine - https://www.uk-racketball.com/promotional-articles.html contact your local surgery and see if you are able to put up a poster and leave leaflets in their waiting room.
The local council is trying to do the same thing that you are. Contact them to see how they can help to promote your sessions.
Many areas have special sport related fairs or have promotions on their websites. This is free advertising and remember that they are natural partners, you are both trying to do exactly the same thing.
Local papers are always looking for new feel good stories so give them one. See if it would be possible to include an article about your Racketball session, include information on the health benefits of the sport, the social side of the sport and how you are looking to grow the sport locally. If you're able to make the article that talks around the Racketball information piece