Regarding sourcing the parts, there are online services available to order 3D-printed parts as you would a PCB. The *.stl files are available in the wiki. Though with how accessible 3D printers have become — the well-supported Ender 3 is available for under $100 at Micro Center — you may want to consider taking up printing as a family activity.
There is a guide available in the repo's wiki: https://github.com/hrc2/blossom-public/wiki
Our contributors' forks and extensions may also be useful:
https://github.com/interaction-lab/blossom-public
https://github.com/interaction-lab/BlossomNav
Regarding sourcing the parts, there are online services available to order 3D-printed parts as you would a PCB. The *.stl files are available in the wiki. Though with how accessible 3D printers have become — the well-supported Ender 3 is available for under $100 at Micro Center — you may want to consider taking up printing as a family activity.