Originally Posted by TokyoSeven
As is to my understanding, you can order them in at your own risk, I believe it has something to do with length, a slide of a certain length is permisable. That is not to say they may not take it anyways.
To add to what TokyoSeven said, slides are importable. Also, prohibited length slides are 4.1" or shorter and might be seized. That being said, I ordered a G26c metal slide and barrel (prohibited length) and it got through fine.