Thanks for requesting me.
As far as removing the magazine catch, lock, and spring goes, the slotted head catch lock only needs to turn 1/4 turn. You might have to slightly push in on the lock a little to get it to turn. When it turns 1/4 turn counter-clockwise, the whole thing will come back out.
Here are the schematics...
Push in a little ways and turn counterclockwise. The lock has a tab that has to go in about 1/8 inch or so before it will turn. Keep pushing in until it wants to turn.
Why do you thing you need new parts?
My power was out due to a snowstorm. Sorry for the delay.
Here is a close-up of the assembly: http://www.m1911.org/technic28.htm
I am having a hard time finding a magazine catch assembly. I have checked all of my resources including Colt. I would strongly suggest that you take it to a gunsmith who can remove it and repair it. That is what I would do for you if I could not find the catch assembly.