I played oblivion for about six months when it came out and never finished it. I only recently started playing it again. I seem to have lost the third mythic dawn commentary needed to complete the quest - I have the fourth so I must have had the third - but i cant find it anywhere. I've checked all the draws in my houses, bookshops etc... but its knowhere to be seen is this a glitch or have I accidently dropped it in the wilderness??? am i screwed?? who knows? Anyway my question is does anyone know if I can get another copy of the third commentary anywhere?
You should have originally gotten it at the First Edition bookstore in the Market district. I don't know about other copies... but if you are sure you had it before you can always add it via the console:
player.additem 00022B06 1 --- Check if you can disconnect the effect and I'll go after the cause