Yes, I managed to lose both dongles for my 2 guitars I use with Guitar Hero Live. Am I required to buy new guitars or am I able to have them replaced somehow? Please let me know soonest.
You can try the Support page to get replacement dongles. Go to this page then click on Warranty > Log-in > Hardware > All Other Hardware then search Guitar Hero Live Dongle (PlayStation 3), PS3. After that, you'll have to submit the entire form including any details of how you ended up losing them and you may have to include the FFC IDs of both guitars from there. The only problem I see with the Support page is that certain countries such as Australia (of which I come from) isn't in the drop-down area listed under Country and I do hope they add any missing countries along with their particular states.