If it's just one domain for one time purpose, it makes no sense you do the full research for this type of domains since it's a lot of knowledge to take care of, and probably a big investment if you are looking for a tool to search for them.
From this point, there are two options
1. Use a tool like ExpiredDomains.net and try to search for a domain name that it's worthy and fits at the same time which is unlikely. I own several dozens of domains and trust me that every time I want to start a new money time, I never find a good domain name that fits, so I end using a seriously weird name that I take as a weird brand (for example, lets say I have a racing domain called f1team.com and I use it just for anything, just simualating a F1 team for whatever)
2. As many has already recommended, ask in the marketplace to any domain seller, but 99% of the time you won't find a useful domain.
So if you care about a brand, just purchase a brand new domain, otherwise, just try to fit the best you can with the best domain you find price/quality wise