A vertical mill, as you have realised, is not really suitable for cutting a rack. It can be done but depends on the DP, the material and how much your time is worth.
1) You can make of buy a right angle drive. (not very rigid)
2) You can use the z axis as a shaper. (not very rigid)
3) You can make a special tapered endmill. (can you make end mills)
I have done none of the above. There maybe others, we shall see.