Hello Steve, there is scant information on Tsugunobu available and you have most of it already. He originally signed Kaneharu and studied under Ryunsai Kanetomo, along with Tsugumasa and other Gunma province smiths. After that he became the 16th student of Kasama Ikkansai Shigetsugu and changed his Mei to Tsugunobu. He was ranked East Block Komusubi in the 1943 Gendai Tosho Banzuke list. His work (published online) isn't seen very often, if you have photos of a sword and Mei I would be interested to see them.
The below is from Malcolm Cox:
The following article has a good deal of information, although the lineage incorrectly placed Tsugamasa under Kaneharu:
https://www.nihontocraft.com/Kanetomo.html
George Trotter and Mal Cox provided the following entries from Japanese sources, included is a nice example in my collection that has a special order Mei: