Most of the manufacturers are based abroad, not difficult to find if you look in the right places.
Most companies only ship by the container full, so you will certainly need a lot of cash input and will need a lot of storage space also.
Then you will need the goosenecks and brushes, tubing and other fittings etc.
I organised the original blue facelift poles for Phil Smith many years ago, it was a very expensive hobby, and difficult to source good suppliers of other bits and pieces.
The tubing in my opinion MUST be on the inside.
Clamps need to be simple to use, and should be adjustable.
Goosenecks need to be available in different sizes.
Brushes need to be available in different sizes.
Pencil Jets
Fans
Microbore?
Good luck and try and think of a good name for them and do your marketing research before you stock up on product.