if they're not supported by your device, then you should find another way to store them.
Yep.
@OP The thing is: to develop HW wallet is quite a hard work. And nobody is going make HW wallet for useless/unpopular coins.
So if you are asking about other coins than BTC (and forks), LTC, ETH .... and few others. You have to use some other wallet. For extra safety you can use cold storage (offline device), or paper wallet.