Generally, it's poor etiquette to request someone's CAD files. If they want them made available, they make them available. And generally a case is specifically designed for the parts that they're using, and so sharing the files could cause more problems than benefits.
If the slot is the only part you're interested in, I'm sure you could design it yourself! It's just a matter of taking dimensions and making a model that works with those dimensions.
I'm sorry if that's so... I'm that kind of Share-Everything-&-Everything-Must-Be-Free-FLOSS-Guy, so I might not have a good feeling/understanding for what people like to share and what not... Now I know how Richard Stallman must have felt in his early days
Anyway.. For me it might be easier to take something existing and frankencase it, than learning FreeCAD >.< .. But I might do it... Hope it turns out as nice as your's!
It's been a while since I've updated this. I'm still working through the CAD model here and there. I've fine tuned the form factor a little further and also the internal component layout. It's probably ready for a prototype assembly at the least I just don't have enough time for all my projects at the moment.