If the two halves have come apart it means the plastic slide has pulled through . I have check my usual sources and there doesn't appear to be replacement parts available. There is quit a few phones similar to this on eBay and Amazon that don't cost much, you can buy one for parts . May actually be cheaper than buying the part new This is a tear-down video .
https://www.youtube.com/watch?v=Kdh0LIOaBB4
You'll need to slow it down if you can. for some reason the poster thought it would be a good idea to speed up the video . hope this helps