A: 
It sounds like your company is being unreasonably strict in its dress policy, but perhaps "business casual" has been wrongly interpreted by some of your co-workers.  By deeming that womens’ blouses should have necklines to the collar bone, they are ruling out the risk of any visible cleavage. 

Unfortunately for you, the v-neck is by far the most flattering cut for a large bust.  Furthermore, to find shells or camisoles that reach the collar bone would be very difficult.  You could try crew neck light weight cotton t-shirts as the underpinning and then let the lines of v-neck blouses or sweaters work to your advantage.  However, this is still not a graceful, figure flattering look for you.

Some blouses the have a higher neck but a loose silhouette (like the example below), which would be pretty with a long, dark wide legged pant  for work (and jeans on the weekend). The key here is to balance the proportions of tops to bottoms to create an overall long line.  Finish off the outfit with big earrings or bracelets to help draw the eye away from the bust.

Long story short, you’ll have to submit to crewnecks and boatnecks to comply with company policy, but you can work within these guidelines to create moderately flattering looks.  Final style tip?  To look your best in these cuts, be sure to invest in very good bras.