Oops. Now, it’s never a good sign if you’re there. I know it can be frustrating.
But! I’ve got a couple of options for you depending on your issue:

Something’s missing

Please email me at nicolas.besuchet@invenart.com. There, mention the part number, quantity missing and delivery address.

A part broke/got lost

Email me (nicolas.besuchet@invenart.com). Mention the part number, quantity needed and delivery address. I’ll give you a quote.
For screws/pins, it shouldn’t be a problem and I could ship quite quickly to you the parts. For the laser-cut parts and 3D printed parts, things could get complicated. Indeed, it takes a few weeks to print (I don’t have one myself. These are industrial printers which cost 100000Euros or so). To top it off, I’d have to reorder that specific part. It’s very much on a case-to-case basis and may take you a month to get your part. Not great, I know.

Something’s unclear

Just email me (nicolas.besuchet@invenart.com). Will be happy to help you out and any of your inputs. This to make things better next time.

Making your own bellow

Bellows are fragile. If you broke it, the good news is that you can make yourself another one. All you’ll need is baking paper (sulfurized paper), a cutter and patience.
There’s how: