vanblah
Short of that, I've had pretty good results with Garritan Personal Orchestra. It contains upbow and downbow articulations as well as many others. It's also fairly affordable.
Doug
+1 to this response.
Your post made me want to double check the Garritan Pocket Orchestra available in Dim. It's a much smaller library than the full GPO, and doesn't have the same keyswitches and articulations available. In fact it operates very differently, in a more generic way.
But the solo strings in GPO have a setting for automatic alternating of bowing, which is what you want.
I did experiment with changing the Pocket Orchestra's solo cello, making the attack much shorter than what's been programmed, and it gave a variation on the sound, more like down bowing.
What's unfortunate is that one of the best sampled instruments ever created, the Garritan Gofriller Cello was only available for a short period of time. It's a highly detailed instrument which can be totally convincing if used properly. It would be ideal for your project. The semi-good news is that you can sometimes find a copy still on sale.
In other words, if you really want to emulate the original sound of Strawberry Fields with a virtual instrument, you'll probably be needing to spend some money.
Randy B.