I doubt you will find a converter.
Why? Because autolisp is on one hand a functional language, on the other it is strongly related to AutoDesk Autocad v 2 till 13, (1986-1995). Thus it is a little bit outdated - although it is still supported in current versions, and used by many.
If you need a functional .net language like lisp, try F# (
http://hammerprinciple.com/therighttool/items/f/common-lisp[
^]).
But if you need to automate a current version of AutoCad in c#, than you will have to redesign and rewrite the functionality from those autolisp scripts to current autocad automation techniques. It is not that complicated (
http://docs.autodesk.com/ACD/2010/ENU/AutoCAD%20.NET%20Developer's%20Guide/index.html[
^]):
http://www.c-sharpcorner.com/UploadFile/sheel_longhorn/CsharpwithAutiCAD01282006002611AM/CsharpwithAutiCAD.aspx[
^].