UAM, SENS and ZOM are are on the NYSE American. I don’t think freetrade have access to this exchange yet (not to be confused with NYSE)
AEI is an Australian company and freetrade doesn’t have the ASX exchange available yet (Europe is their next move)
The others you can request Freetrade New Stock Request Form
Most other brokers have been around for decades and have built up their exchange availability, or in some other cases they pass off trades to a third party broker.
If you do look to open an account be sure to read the terms. they’re non standard.