Getting late for tart/sour cherries, at least here as picking started in mid-June at our local PYO orchard. Check with Cold Spring orchard (U. Mass/Amherst). Google pulls up several other possible sources in that area too but again, picking is already well under way since early July.

Dave

Here is a link that might be useful: Cold Spring Orchard

Another avenue might be asking around at a local Farmer's Market. I found a source for local sour cherries by asking a fruit vendor - he didn't grow them anymore, but he knew someone who had three or four trees producing more than the friend personally could use or share.

Might be worth asking about for next year.