homebrew hood
If you want to humor yourself and make a homebrew one fro ma plastic bottle, the last two vitamin bottles (250 count) I checked had 37.7 - 38.5 mm openings. This has been documented elsewhere, possibly Bob Monahan's MF site and a FSU camera site as well.
It'll work for a standalone hood, but may not be very accommodating in combination with filters
There are spray paints nowadays that will stick to plastics (check label) without dissolving them, although I haven't found a flat black compatible with plastic yet.
I will be doing this for an Aga Solinar 37 mm diameter push-on hood soon.