If I remember correctly there is no limit, wiki says same. 2 chests have a possibility to drop them. Just try more often till you get them
For anyone who might be interested in getting multiple pairs of ruined dragoon boots I was able to get my first two pairs after 6-9 runs. I was able to get the third pair after another 9-11 runs.
The drop rates do appear suspect though. A partial list is as follows: ruined dragoon boots (%22.4), demonic skull (%17.6), ring of the red sorcerer (%13.7) and blessed platemail boots (%12).
I literally have 5 demonic skulls in my inventory from this run series. I sold at least 3 ring's of the red sorcerer and 3 blessed platemail boots during the same run series. If the drop rates are accurate then I'd expect to have almost twice as many ruined dragoon boots as blessed platemail boots.
Thanks to this thread I was able to verify that there is no limit on the number of dragoon boot drops. Then it was just a matter of persistence until I hit the number I wanted.