G'day Twitchy
Missed your OP the other day
I have this issue regularly when shooting at >300mm & there are no ready-made lens hoods to suit my stuff ~ so I made my own for <$15
here it is...
a plastic drinking glass [$2], the bottom chopped off and sanded smooth, then epoxy-glued to an old UV filter metal thread [glass removed] and painted internally with blackboard matt black paint
Works a treat covering the 300 - 450mm range of the lens
[ps- all lens-maker-supplied lens hoods for a zoom lens are only designed for use at the wide-angle end of the lens - out from this, the lens hood rapidly loses effectiveness]
Regards, Phil