| Do you know any long range wireless communication gadget (radio modem etc.) | that can be used for 115200 bits/sec continuous data transfer over 100 km ?
Yes, radio modems do exist that can do 115 kbit/s. And radios do exist that can work across 60 miles, though that's generally more than line of sight unless you have a tall tower for an antenna, though if your plane has considerable altitude that'll help.
However, to get that sort of range, especially with it being that close to the maximum line of sight, you'll need either a reasonable amount of power, and/or good directional antennas. Both will be difficult to set up on a standard sized model plane.
Also, you'll either need some dedicated bandwidth, or a ham license. The former will be difficult for an individual to get. The latter is pretty easy to get, but it limits what you can do with the link.
You could use the 900, 2400 or 5800 mHz bands, which are available for use without a license, and cheap equipment exists that will give you much better than 115 kbit/s connections over that, but the power limits are so low that you won't even get a single mile of range without great effort.
Another option is a satellite link, which is what the TAM team did when they crossed the Atlantic -- though their plane was autonomous except for takeoff and landing, and I'm sure the data rate was MUCH less than 115 kbit/s. You could also use standard cell phones with data services if you're flying over areas with cell phone service. Might not work if your purpose really is emergency use, however -- emergencies tend to take out cell phone service.
| (Imagine you are on a boat/ship and you have a UAV. You want to fly | your UAV to 100km away and you want continuous comm with the | UAV. Because one end of the communication is an small airplane the | smaller size and lighter weight for the gadget are peferred.)
Lots of people have experimented with this sort of thing with various budgets and various degrees of success. Google will probably find you lots of stuff.