this converter converts anything to anything. (well almost everything) http://www.erightsoft.com/SUPER.html
I just found a flv converter at http://www.freedownloadmanager.org/downloads/Moyea_FLV_to_Video_Converter_41506_p/ it may help you!
...And if you wish to do the .flv to 3pg conversion online and free, check out Media Convert. Supports an enormous list of input formats.
downlod the software for it from download .com and u will get many softwares and u will do your job easily