Given they fact that your Father has MS, I would think your Mother would be MORE understanding about you wanting to get to know him if only for medical reasons.
I am sure she is trying to protect you but its time to help rather then protect.
As Travelinggal suggested, you can check out
Find a Person or Business with our free online White Pages and Yellow Pages and just start calling and asking questions. If you aren't comfortable spilling that your looking for your Father, you can use the phrase "I'm doing genealogical research and I came across this name". Thats what I used when I was looking for my biological Mother.