REQ - plastic sleeve with 4 smaller tubes running part-way through

The part is basically a plastic sleeve, which fits over a metal gas cartridge, with 4 separate tubes or "barrels", each holding 3 plastic bbs as per this image:

Attachment 18102

Loaded:
Attachment 18103

Whilst I can purchase more of these sleeves in the current dimensions, what I'm after is someone who can make them so they would be the same overall length as this shell:
Attachment 18104

The pink shell is approx 1" longer and only has 1 tube or "barrel" running through it so what I'm after is a black-style sleeve that still has 4 tubes within it but is the same overall length as the pink shell. The tubes running through the black sleeve don't run all the way through as this would interfere with the gas chamber that it slides over.

I have each shell type so can supply for measurement/inspection purposes and am looking for someone to have a crack at a prototype black sleeve (doesn't have to actually be black plastic) and, once working would result in an initial order of a few dozen with potentially a few hundred thereafter.

Hope someone out there can help.

Many thanks for reading.

I've been informed that the attachments aren't working so will try to fix this after work today.