I know I am quite late at answering this, but Photoshop now does have an automerge function which can stitch images as you like.
As you had mentioned in the comments you just have issue with the camera stitched images and the individual images are fine. The process to do so in Photoshop is,
Open all photos in Photoshop as either jpg or psd, but I'll suggest to keep them as JPEG or jgp and not PSD because then you will use more storage
Go to file, automate, and select auromerge.
Wizard box opens, add all open files to the wizard files. Select the settings you want.
Wait for it to process. Fyi: if the images are individually very high in size and pixels, it will take time depending on the processing capacity of the computer. So just wait, have a coffee.
Check the resultant merged file. If not proper or as required then try to club/group them according to the content of the images. Because that's what Photoshop does. And repeat the same set of tasks with the groups you made. Then merge the final merged file from groups!
I hope this does help someone.
I did read the post again, yes you do not have the original photos of the panorama, but maybe try this (would be only feasible and logical if you don't have many blurred parts in the image).
1. Crop the original stiched photos in Photoshop in pieces with edges being the parts where you feel highest distortion or blur.
2. Fix these images using selection tools, transform tool and make a perspective transform of the blurred parts
3. If you are somewhat satisfied with this, go ahead and use auromerge from Photoshop.
This may to some extent reduce the visible distortion/blur but if you wish to get a very high quality print or submition this may not work 100%.