Replay A/V's URL finder doesn't work with a dial-up connection so I can't test it, but their friendly support will definitely help. Actually it is always better to try the latest version before asking...

I use free Project URL snooper to find stream URLs

Can't tell you anything about Riva Player. I actually suggest other software for playing .FLV files. ATM I use free "K-Lite Codec Pack" to play flash videos by any direct x based video player. This codec pack has an FLV splitter and it uses ffdshow decoder to decode video stream on my PC. Free Media Player Classic that comes with it is one of the best video players available. And IMHO it is the best way to play .FLV files, 'coz other players were not as good in my tests.