Mp5k as sidearm

Hi all, i have a mp5k laying around, and its hard to use it as a sidearm without a proper holster, so i'm asking what would be the best way to make one, or can i buy a big holster and modify it for mp5k.
Ps. There is a army stuff shop with huge amount of old army stuff etc, so if you know some old army holster/etc, that could fit a mp5k, tell me.