Although the discussion took place few years ago, I would like to make some corrections for future readers. Tikapatthana in this case means not a subcommentary, but the first division of all Patthana. Here Tika means "three" and this part of Patthana consists of 22 tikas (triplets) which are given in the Matika (Table of content) of the first book of Abhidhamma titled Dhammasangani. The second part of Patthana is Dukapatthana, which deals with 100 dukas (couplets). The other parts of Patthana are combinations of these tikas and dukas.
All Tikapatthana is translated into English by Sayadaw U Narada and published by PTS. Since 2013 PTS kindly granted its permission for free non-commercial distribution of all its translations of Abhidhamma. You can find pdfs of Tikapatthana in English at www.patthana.net
as well as many other materials on Patthana.