You can also go to garywillis.com(Gary Willis was probably one of the first to use a ramp) and use the "Ask Willis" function to send him an email, he usually answers within 7-10 days.
Search the archive on his website, I'm sure someone has already asked him re the ramp. AFAIK
the answers are public for everyone to read.
I used to have a ramp on my old 5-string, custom made by the guy who built my bass. Any good luthier should be able to custom build it for you.