I have not seen this variety either, but we have similar drawn striped beads in our Museum.
The ones in the picture are from the African trade.
The top and middle strand have a grayish blue core; the one below is plain white with pink stripes.
I think the beads in the middle strand are the same as the ones showing on the “beads traded for palm oil ”card in the British Museum. (left column, row 9).
All seem to have less stripes than the strand you are showing. sizes varies between 6.5mm to 12mm
I would guess they were made between 1800s to early 1900s
JP