I love those Titan split covers, but they never ended up selling posters of them, which was a shame. And I offloaded my copies when I decided to not have multiple copies of comics (as it was getting expensive and taking up too much space), and preferred to keep the original single issues.

It was difficult finding the combined cover images online too... and the ones I did find were small.
Books 1 & 2
Books 3 & 4
Books 5 & 6
Books 7 & 8
Books 9 & 10
That site has been adding them over the last few weeks, so might add the last three (there were 16 covering the Gen1 & Gen2 US Comics).

Maybe you could see if anyone here who has the whole set could post up decent sized scans of the covers, and you could combine the images yourself?
TFwiki has details and small images of each Titan book, as does TFArchive.