Yeah... The problem is that the Amiga outputs video modes that are half the refresh frequency of VGA screenmodes. This is not an easy problem to compensate for.
The silver "VGA Adaptor" that most people sell, are not VGA adaptors at all. They simply change the plug from Amiga DB23 to PC HD15. As Redrum said, these can be built or purchased very easily, but they won't really help your problem.
Your problem is, that the video signal from the Amiga is not within VGA specs. In order for games/demos, etc to work, this can only be fixed by a complex (and expensive) "scan doubler."
If you only want to see Amiga Workbench, you COULD install the ECS Agnus/Denise combo in your A500, cut a couple traces, and then run OS 3.1 in productivity modes... But that's probably not the solution you are looking for...