A quick search lead me to these sites, which I guess will do the job, but I haven’t verified if they’re working or not. It seems at least some of them will add some public trackers to the magnet link, but, with DHT enabled in the client, I think it could also work without adding those.

www.hashtomagnet.com magnetlinkgenerator.com hardrisk.github.io/magnet/

hash2torrent.com/{info-hash} (replace with the actual hash without the curly brackets to get the torrent file)