Keyboard lockouts - this allows inadvertent pressing of keys while in the flight. Dual band radios, as mentioned above, can operate like repeaters, i.e. receive on one band and transmit on another. Since a repeater transmits on one frequency and receives on another, your radio must be able to do the same. Even though this is standardized, there are some non-standard repeaters in the world. Some radios permit non-standard offsets.
Mail order is probably the largest source of products.
Another great source for buying equipment is Mike Kelley at Kentuciana Soaring. Mike is a hang gliding pilot who not only knows what you need, but he has a reputation for beating your best price. The Ham community knows where and when the next one is. They're great fun, and full of fantastic bargains. Another important part of your radio is a holster.