I went through this search years ago and was determined to solve it.
Back then even the cheap Amazon crap gas jugs were not available in 2.5 gallon yellow so I contacted the manufacturer of the 5 gallon jugs but they were not interested. I asked if I could hire them to start making them for me on a high volume basis and I would become the distributor but again, zero interest from the manufacturer.
This I could not understand. They have the molds, they have the process and equipment; All they have to do is change the colour of the plastic, but no, zero interest.
I then looked into having my own molds made but quickly realized the costs of the molds and safety certifications, insurance etc were beyond me. If you ask me, they missed an opportunity and it would seem that the Amazon jugs prove the demand is there.