Something I had meant to do, when I wrote about the catena of Nicetas, was to track down the works of J. Sickenberger mentioned as published in TU. I have, in fact, now updated that page with some links to Google books, although, as ever, non-US readers will not be able to read them.
TU 21.1: J. Sickenberger, Titus von Bostra. Studien zu dessen Lukashomilien (Leipzig, 1901) can be found here. This is not evidently about the catena on Luke by Nicetas, except that Titus of Bostra figures regularly in catenas, including that of Nicetas.
I have also updated both Google books pages with a “review” indicating the contents of each volume. That should make searching easier!
But how did I find them? Through a link to the right here, which I often use. Mischa Hooker compiled an index of TU volumes 1-32. It is such a useful resource!
My main remaining problem is that my German is not that good, and academic German of a century ago is pretty impenetrable!
The final item mentioned is Sickenberger’s 32 page monograph, Aus römischen Handschriften über die Lukas Katene des Niketas (1898). This is referred to here. But I was unable to locate the item itself. I suspected that perhaps it too was part of a serial. And a Google search indicated just that: “Röm. Quartalschrift für christl. Altertumskunde und für Kirchengeschichte, XII ” (don’t you just hate that habit of abbreviation?). I think it’s actually known as “Römischen Quartalschrift”. But I had no luck finding that volume online.
UPDATE: Now running OCR using Adobe Acrobat on TU 22.4. The only way I shall be able to work on that will be with the help of Google translate!