That's a very generous present and it's very kind of you.
I assume you are sure that your boyfriend really wants a Gretch guitar?
The thing is though, he (as the player) really needs to choose the guitar for himself. Even if you know the exact model and colour of guitar he wants you could find three or four of them, even in the same store, that felt and played differently. One might be virtually unplayable, two might be okay but one might, to your boyfriend, be perfect.
I'm in the UK and we don't have Guitar Center here but, really, you're as likely to find a guitar that suits your boyfriend there as anywhere else but, he really needs to try it first. Otherwise there is a risk that he gets a guitar that is unplayable or that he doesn't like.
Also, and please don't take offence, it is possible that as someone who doesn't appear to know a lot about guitars, you might be offered a guitar that staff know is not a great example.
Like I say, it's a great idea for a present and he should be thrilled, but take him with you to choose the guitar.