Does anyone know where I can buy baroque music printed at baroque pitch rather than modern pitch? It would be useful to give an accompanist rather than relying on him transposing.

I somehow doubt you can get it because the whole thing about baroque pitch is that the notes are the same but the sounds are different. You could scan it into sibelius and transpose it down a semitone though I think. Not sure if that's legal though.

As sarah said, the notes are the same, a scale of c major in baroque pitch is still CDEFGABC written down, but it sounds 35hz lower than that, so slightly flat, its not quite a full semitone though (i think) so if you transpose it, it might not sound right either.
If its an important recital your giving, you could always ask the piano be tuned to A=415, although its unlikely.

buy the normal music, then take a pen and write in "A=415" at the top of the piece. now it's in Baroque pitch.

But, of course, there were a number of Baroque pitches (as well as temperaments) depending on location....

Perhaps singing nurse ought to get her piano (if it's permitted to use a piano for Baroque music) tuned to an unequal temperament as well as having the pitch changed!

Yes, get a modernly tuned harpsichord, then get out your boyfriends/fathers/brothers/neighbours ratchet set, and turn a few of the little pegs toward the left, some to the right (but not too much, lest you break the string) and leave the rest in place.
You have baroque pitch.

If you want to be able to alter pitches perhaps use a digital piano with a tuner. Many of these have passable harpsichord voices too. I have used mine in exams many times.

Some sophisticated models let you use different temperaments too.