It's not strictly about the Ikkō-ikki but The Culture of Civil War in Kyoto by Mary Elizabeth Berry (ISBN 978-0520208773) contains several chapters discussing the ikki movements and their affect on the Kyoto area. It treats them more as some groups among many than being specifically about them, however. Similarly, Suzanne Gay's The Moneylenders of Late Medieval Kyoto (ISBN 978-0824824617) also has a lot of detail about the conflicts between urban moneylenders and the ikki movements which tended to be comprised of peasants, many of which were in heavy debt to the moneylenders.

Neither of these go into great detail about the great mountain temples or the warrior monks (sōhei) themselves. The obligatory wikipedia page has some resources which look to be more directly about the movement themselves.