Have you looked on Gunbroker. There are several slides and parts kits listed.
Slides
https://www.gunbroker.com/Gun-Parts/search?Keywords=bersa%20380%20slide&Sort=13&PageSize=48
Parts Kits
https://www.gunbroker.com/Gun-Parts/search?Keywords=bersa 380 parts kits&Sort=13&PageSize=48
Slides
https://www.gunbroker.com/Gun-Parts/search?Keywords=bersa%20380%20slide&Sort=13&PageSize=48
Parts Kits
https://www.gunbroker.com/Gun-Parts/search?Keywords=bersa 380 parts kits&Sort=13&PageSize=48