Ebay is full of adapters that you can use..
http://cgi.ebay.com/VGA-MONITOR-ADAPTOR-FO...1QQcmdZViewItem
I've never personally seen THAT one, but it seems to be pretty nice. But as is says you will need to know if your 500 has a denise or super denise.
Also ebay is full of those 520's... Here are the specs:
* video modulator allows TV sets to display Amiga graphics
* provides a standard UHF RF output as well as a standard composite video output
* three RCA connectors:
o RF output
o colour composite output
o mono audio input - connected to the stereo Amiga output with an Y-cable
* channel selector switch
* atrocious video quality
* PAL and NTSC versions
Also genlocks might do the trick for you as well, search ebay for those.