Where can I buy wireless transmitters online?

Yes but only if the hi-fi unit either has a built in wireless transmitter or the wireless speakers arrived with a dedicated sender unit to plug into the hi-fi or tv or whatever you need to use them with.

I suggest you begin by reading the two relevant instruction booklets or finding the specifications online.
If there is no sender unit it might be possible to buy a generic wireless sender unit.

if you want to burn up the headphones and buy new ones,go ahead,

if a car uses regular gas,do you fill it with diesel???

• Goodmorning, I received Slick HP921 Wireless Headphones yesterday I have perfectly utilized them yesterday but today I have no communication between the wireless transmitter and the wireless headphones without changing anything since yesterday.
  The wireless transmitter is turned on but it's not trasmitting. The headphones work perfectly with fm mode and also when i connected the single green plug with other devices ( pc, phone ).
  The problem should be in the wireless transmitter.
  What I have to do ?
  

http://www.amazon.com/Gamecube-Wavebird-Wireless-Controller-Platinum/dp/B00005BOSF
I hope this will help.

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I've had to order them from AKG - you might check Guitar Center and or Musicians Friend online

if most repair shops cannot fix it, and it has been discontinued, then it would probably be a good idea to buy another set of wireless speakers. you might wanna try looking at reviews for different ones on the internet. CNET, youtube, and other places are good places to look for some

Buy a new one. & dont forget to check this time ;)

If you're handy, you could rig up a wireless solution to this. The problem is that you have two screens, each presumably playing a different movie. If you purchased an off-the-shelf wireless transmitter accessory, you could connect it to one of the screens. But then if you purchased a second wireless transmitter accessory, and connected it to another screen, you would need to make sure both wireless transmitters were operating on different frequencies, so that each person could wear a different pair of headphones and listen to their own movie. Hopefully this makes sense. You could use either an FM Modulator to do this, or an Infrared Audio (IR) transmitter... Remember, these units aren't like factory installed headrest systems; they don't have the wireless audio transmitter already built-in, so you can't just buy wireless headphones and listen to them.