I have completed the thieves guild questlines and have completed the city influence quests to become head of the thieves guild. I missed obtaining the model ship during the normal quests. I went back and found it but delvin will no longer accept it. Is there a way around this?

There's been a few glitches with those larceny items. Everything from only six out of the seven items count as quest ones, you have to turn them in the right order, you can only turn them in before finishing the critical path Thieves Guild quests, etc. If you're already past the Thieves Guild questline in its entirety, you're likely stuck with the boat.

Oh well. I guess it will make a nice addition to my bathtub at Proudspire Mansion